Capabilities
Autodesk River Analysis completely automates HEC-RAS within AutoCAD Civil 3D and Map 3D. Both US and metric (SI) units are supported.

1.1.1

Easy Model Development
Autodesk River Analysis is easy to learn and use. Even without any previous AutoCAD experience, you can become productive quickly. Customized dialog boxes and command prompts make data input simple and intuitive. Pop-up menus bring commands immediately to your fingertips and context-sensitive help is always available—even midway through a command. You can use Autodesk River Analysis with your existing AutoCAD drawings. After a surface has been created in AutoCAD Civil 3D, river modeling data such as bank station locations, flow distances, ineffective flow areas, levee stations, Manning’s roughness sub-areas can be quickly extracted from the drawing. The HEC-RAS model

runs directly within the AutoCAD environment, and the computed analysis results are displayed directly in the AutoCAD drawing. Floodplain and floodway mapping, base flood water surface elevation (BFE) contours, flow depth contours, cross section plots, and profile plots can be displayed in the AutoCAD drawing, quickly plotting the model results for you. The completed HEC-RAS model can then be exported for agency submittal.

1.1.2

Automated Terrain Data Processing
Autodesk River Analysis takes complete advantage of digital terrain mapping automation to instantly extract cross sections, land use data, Manning’s roughness, channel and overbank flow lengths, bank stations, ineffective flow areas, levee locations, and other terrain data into HEC-RAS. Using the software’s terrain processing capability, a river model can be developed from any type of digital data, including 3D digital contour maps, TINs, DTMs, DEMs (digital elevation models), LiDAR, 2D digital contour maps, hard copy contour maps, hard copy cross-section plots, on-screen digitizing, manual data entry, and importation of complete or partial HEC-RAS or HEC-2 input files, station-elevation, Northing-Easting, or XYZ coordinate data. This allows you to construct, analyze, and display the analysis results for a HEC-RAS model for several miles of river in just minutes. Several orders of magnitude increase in productivity is achievable using Autodesk River Analysis.

1.1.3

Automated Floodplain Mapping
Once the HEC-RAS analysis has been performed, Autodesk River Analysis can generate a detailed floodplain map of the computational results—showing the extent of the flooding on the AutoCAD drawing. Very precise edge of water mapping is created—greatly speeding up the process of creating final map submittals for agency review. The software automatically generates approximate (FEMA Zone A) and detailed (FEMA Zone AE, AH) flood maps. Water surface elevation contours, commonly called BFE’s (base flood elevation) contours, are automatically constructed and labeled. Flood depth contours can be generated in order to create flood hazard mapping. You have total control over line style, line color, line weight, hatching, and other drawing configuration parameters in order to meet any specific corporate CAD drafting standards.

1.1.4

Automated Floodplain Encroachment Modeling
Autodesk River Analysis reduces the time for computing floodplain encroachment stations—typically an extensive time-consuming process—to just minutes. You can quickly iterate encroachment station locations—while simultaneously reviewing the incremental water surface rise, floodway top width, and flow velocities at each river cross section and on the topographical map—to provide the best land development solution. The software allows you to maximize recovery of land for development— gaining significant acreage for your clients in just minutes of work. Once the final floodway locations have been determined, the required HEC-RAS model files can be instantly exported for FEMA submittal along with the completed AutoCAD drawing.

1.1.5

FHWA DOT Bridge Scour Analysis and Reporting
Our software development team worked with several major engineering companies involved in FHWA and DOT bridge replacement contracts to completely automate the analysis, design, and reporting necessary for bridge replacement and scour projects.

showing whatever variables you select.9
Model Checker
Autodesk River Analysis includes a built-in Model Checker. and displaying HEC-RAS models. intermediate results.8
River Scenario Analyzer
The River Scenario Analyzer allows you to quickly compare HEC-RAS analysis results—examining the output at any level of detail required. Once a customized output layout has been defined. it can be saved as a template for later use. allowing you unlimited flexibility. If it encounters an error. variables.Overview
1-3
Autodesk River Analysis can analyze a bridge for scour and create a “ready-to-submit” FHWA-accepted bridge scour engineering report in just minutes. which enables you to import and export HEC-RAS model information without any loss of data. The scour report includes all input data.
.7
AutoCAD Integration
Autodesk River Analysis operates directly within AutoCAD Civil 3D and Map 3D. Customization of graphical plots and output tables is supported. and analysis narrative—along with placing the computed scour results directly on the bridge within the AutoCAD drawing. metric. and abutment scour effects US. equations.1. with a single mouse click your completed model can be exported ready for agency submittal.
1. The Model Checker analyzes the input data for any modeling errors. With the River Scenario Analyzer you can generate report quality charts and plots that are customized specific to your needs.1. it explains what is wrong and suggests possible corrections.
1.1. The scour analysis can account for the following factors: • • • • • • • • • Bridge skew Pier skew Pier shape Sloping and skewed abutments Soil bed material Armoring of bridge abutments Armoring of bridge piers Contraction. or mixed unit-based input data
1. This provides you with a high level of precision by leveraging AutoCAD Civil 3D and Map 3D automation capabilities in constructing. And.6
HEC-RAS Compatibility
Autodesk River Analysis fully supports the latest version of HEC-RAS. final analysis results. analyzing.1.
1. pier. Multiple graphical plots and output tables can be stacked on top of each other.

Organizing the drawing by using layers allows various elements and
. and energy grade line elevations on the cross section grids. the software can overlay the water surface profile on top of the contour map. It can display the computed water surface. discharge. XYZ coordinate data.
• •
After the model has been properly defined. A river model is developed by: • Defining cross section locations and the corresponding ground geometry using any combination of 3D digital contour maps. the water surface profile analysis can be performed. storing various entities on their own layers. All modeling data is stored directly in the drawing file as custom entity data. split flow conditions. and split flows. The software reads and writes data from the latest versions of HEC-RAS. flood plain reclamation. critical water surface. on-screen digitizing. starting elevation. and importation of complete or partial HEC-RAS data sets. Defining any floodplain encroachments. there are no external files to maintain. USGS DEM (Digital Elevation Map) data. This section gives an overview of this application.Using the Program
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C H A P T E R
Using the Program
2
Autodesk River Analysis is an advanced river modeling software that completely supports HEC-RAS within AutoCAD Civil 3D and Map 3D. 3D digital terrain models.
2. stream realignments. spillways. The software uses AutoCAD drawing layers extensively. and other necessary parameters.
2.1
Program Overview
This section provides an overview of the major elements of the Autodesk River Analysis user interface.). culverts.. etc. The software makes it easy to compute water surface profiles for modeling bridges. In addition. 3D TINs. showing the extent of the water surface with regard to the ground topography.e. Since these various grids are contained within the AutoCAD drawing file. importation of complete or partial HEC-2 input card files. After the analysis is complete. providing you with a fundamental understanding of the operation of the software. manual data entry. floodway delineation. bridge scour. hard-copy cross section plots. stream diversions. and other items that the model is to include in its analysis.1. they can be quickly annotated with descriptive notes and drawing details. stream restorations. 2D digital contour maps. profile grids can be created. hard-copy contour maps.1
Background Information
Autodesk River Analysis operates directly within AutoCAD Civil 3D and Map 3D. levees. Defining the starting water surface profile conditions (i. bridge and culvert structures.

storing various entities on their own layers. When AutoCAD commands (such as MOVE) are used. entities created by Autodesk River Analysis are drawn on these layers. Autodesk River Analysis drawing layers are labeled starting with C_RIVR.2. click River tab > Create Reach Data panel > Create Reach Data drop-down > Reach Information. letting you view and plot them separately or in combination.2
Drawing Layers
Autodesk River Analysis uses AutoCAD drawing layers extensively.3
Model Information
Information about the current analysis model is available in the Information dialog box.1. rescaling.
2. select the River Analysis workspace. Therefore. entities can be modified as other AutoCAD entities. and Deleting Entities
Autodesk River Analysis uses custom entities. copying. When the River Analysis workspace is active. and reactors to store and manage HEC-RAS and HEC-2 data within the drawing.
.
2.3
Application Tools
Autodesk River Analysis includes many useful computation. and deleting entity data.2
Accessing Commands
To access the Autodesk River Analysis tools in AutoCAD Civil 3D or Map 3D. and editing tools.2-2
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
components of a drawing (for example.
2. The River tab provides tools for moving. and other information related to the model.2. By default. the entity data and drawing file might become corrupted.
2. display. The Information dialog box displays information detailing the HEC-RAS model assigned to the current river reach. Modifying. cross section reach lengths) to be turned On and Off. the starting and ending cross sections. River Analysis entities are not dynamically updated.
2. Do not modify the layer names.1
Moving.
2. object dictionaries. If the layer names are changed from the default. It reports the number of cross sections defined.2
Application Basics
The following sections discuss the application basics of Autodesk River Analysis. select the River tab. drawing. NOTE: Related River Analysis entities are dynamically updated only when they are edited within the River Analysis commands. To display this dialog box.1.

Alternatively. On the View Reach Extents dialog box. Selecting a Section To make a cross section current. select a cross section to make current and display on the screen. select the appropriate profile view. click River tab > Navigate panel > Zoom to Reach Extents. then this display will be maintained. The selected section ID is displayed in the list on the Input panel. select the section from the cross section list on the River tab > Input panel.3. Zooming to a Section Location on a Surface To zoom to the current cross section’s location on the surface.
Navigating Among Cross Section Grids
To view cross section grids for the current river reach in ascending or descending order. it is necessary to first select a cross section before editing its corresponding data. Zooming to Section View To zoom to a section view.2
Viewing the Extents of a River Reach
To view the extents of a river reach. click River tab > Navigate panel > Zoom to Profile View.Using the Program
2-3
2. enter RMS_XSSelect on the command line. On the Zoom to Profile View dialog box. This command is similar to the Zoom to Section View command—except that the display is not altered.3. click River tab > Navigate panel > Zoom to Section View. select the appropriate river reach. From the Select Cross Section Grid dialog box.
2.
.1
Selecting and Viewing Cross Sections
All cross section data editing occurs on a single cross section basis.3.3
Viewing a Profile View
To view a profile view. In the Zoom to Section View dialog box. click River tab > Navigate panel > Zoom to Section Surface. select the cross section to make current.
2. enter either RMS_XSPrev or RMS_XSNext on the command line. If you are currently looking at a different cross section or a topographical map view. Therefore.

Accuracy (optional) This entry specifies the accuracy desired when computing normal or critical depth. This entry is not required and will be ignored when computing normal or critical discharge. click River tab > Analysis panel > Hydraulic Calculator. Discharge This entry specifies the flow discharge when computing normal depth or critical depth for the currently selected cross section grid.2-4
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
2.01 meters). Calculate Property Select the property to be calculated: • • • • Normal Depth Normal Discharge Critical Depth Critical Discharge
Depth or Elevation Either the Depth or Elevation fields can be used to specify the water surface when computing normal discharge or critical discharge for the currently selected cross section grid.3. This entry specifies the accuracy in feet (or meters). Reset Resets the Known Values to their default values. Gradient (optional) This entry specifies the energy gradient to use in the conveyance calculations. the software automatically determines the bed slope of the upstream reach and will present this value as the default energy gradient. and the default accuracy is 0.
. Click Pick to select a water surface elevation from the cross section grid.01 ft (or 0.4
Hydraulic Calculator
It is often useful to compute the normal depth at a cross section for a given discharge. The Hydraulic Calculator computes the following hydraulic properties for the currently selected cross section: • • • • Normal depth and corresponding elevation for a specified discharge Flow discharge for a specified normal depth or elevation Critical depth and corresponding elevation for a specified discharge Flow discharge for a specified critical depth or elevation
To open the Hydraulic Calculator. The following paragraphs explain the options that are available in the Hydraulic Calculator dialog box. When the Hydraulic Calculator dialog box is first displayed. Specifying a value in this entry allows you to override the previously determined energy gradient value.

critical. subcritical. However. Use the boxes in the Report? column to select which results are to be included. based on the specified parameters. From this area.Using the Program
2-5
Compute Performs the hydraulic calculation. click Print to print the results. You can repeatedly use the Hydraulic Calculator to place multiple analysis results on a cross section grid. Should this occur. or supercritical) Flow area Wetted top width Average velocity Maximum velocity Composite roughness Critical slope (for normal depth and normal discharge calculations only) Hydraulic radius Wetted perimeter
The Hydraulic Calculator displays the analysis results in the Calculation Results area. It then sums together all roughness subarea conveyances to determine the total conveyance for the cross section.
Numerical Basis
The Hydraulic Calculator uses Manning's formula to compute the conveyance of each roughness subarea for the current cross section. the Hydraulic Calculator reports that it was unable to converge to a satisfactory solution. an iterative process is used to compute the flow depth to the specified accuracy. the analysis results can be placed into the drawing adjacent to the cross section or printed out. Click Erase to clear any previous analysis results from the current cross section grid.e.. Calculation Results The Hydraulic Calculator reports the following additional hydraulic properties after performing its calculations: • • • • • • • • • • • Energy gradient used Froude number Flow regime (i. Or.
Flow Depth
In computing the normal or critical flow depth for a specified discharge. Click Place to position and place the results adjacent to the cross section grid and automatically superimpose the computed water surface upon the cross section geometry.
. try using a larger accuracy value. if the computed flow depth cannot converge to the specified accuracy after 100 iterations.

It knows nothing about ineffective flow areas.
. as shown in the following figure. the first and last cross section in a river to be modeled will correspond to either the start or end of a particular reach.
Energy Gradient
The software automatically determines an energy gradient value to use when the Hydraulic Calculator dialog box is first displayed. However.
Available Flow Area
The Hydraulic Calculator considers the entire cross section geometry as available for flow in its computations. this computed value may not be representative of the actual energy gradient and could adversely effect the conveyance calculations. However. split flow reaches. In other words.
Critical Slope
When computing normal depth or normal discharge. the computed energy gradient should be checked to determine whether it is a reasonable value.2-6
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Flow Velocity
In computing the average flow velocity. A river reach consists of a set of related cross section grids. The software uses the minimum elevation at the current and adjacent upstream cross sections and the channel flow length to compute an approximate energy gradient. it does not adjust the wetted perimeter to account for the addition of these vertical walls. If either the starting or ending cross section stations are below the computed (or specified) water surface elevation. The velocity of each roughness subarea is also determined. floodplain encroachments. However. Therefore. Reaches start or end at locations where two or more streams join together or split apart. it should be modified. the Hydraulic Calculator assumes a uniform velocity distribution across the entire cross section. profile grids. Therefore. Reaches can also start or end at the open ends of the river system being modeled. This value is determined by dividing the discharge by the total flow area.
2.4
River Networks
A river (or stream) network can be represented by a set of interconnected river reaches and connecting junctions. and if not. the Hydraulic Calculator will automatically extend wetted vertical walls to contain the computed flow. and associated data which define the model. or overbank areas in which divided flow has been restricted. At a minimum. only the maximum velocity is reported. the reported critical slope is the channel bed slope that would cause critical depth to occur for the specified (or computed) discharge value. each river reach must contain at least two cross sections. use caution when applying the Hydraulic Calculator to these special situations.

each model is defined as a river reach.4.
Multiple HEC-RAS Models
The software is capable of managing several separate HEC-RAS models within a single AutoCAD drawing file. and it can be moved about the drawing or hidden.1 River network is represented by interconnected river reaches and connecting junctions
Each river reach must have a unique name. and is identified by a the reach name and a unique ID. The process for managing these reaches and junctions is described in the following sections.Using the Program
2-7
Figure 2. When multiple river reaches exist in a drawing. allowing you to perform several separate water surface profile analyses within the same drawing. Each connecting junction is also represented by a unique name. In order to these separate models.
River Reach ID Marker
Each river reach has its own ID marker in the drawing. the current river reach is easily determined since its identifier is circled on the drawing as shown in the following figure. A river reach ID marker is placed at the most downstream cross section used in that river reach.
. if desired.

At least three river reaches are required to define a junction location. for small projects involving a single river reach. click New. The Junctions dialog box is used to define the reach data that details how the river reaches join or split apart. as your expertise grows and more complex modeling within a drawing is required. you might not know that river reaches even exist since the software automatically manages all aspects of the initial river reach. But. To create a new junction. in the Junctions dialog box.
Management of River Reach Data
River reaches may be a difficult concept to understand initially. The Junction dialog box creates a blank junction entry.2 The river reach identifier (diamond symbol with circle) is placed near the downstream most cross section
River Reach Information
The Information dialog box describes the current river reach. enter RMS_Info on the command line. However. To display the Junctions dialog box.2-8
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Figure 2. allowing you to define the data describing the
. including upstream and downstream cross section IDs. no user interaction is required to set up or manage the river reach. as well as ground geometry extents for all cross sections in the current river reach.4.1
River Junctions
A junction is a location where river reaches join together or split apart. To view the Information dialog box. In fact. but are extremely powerful and provide great modeling flexibility.
2. river reaches will prove to be invaluable at managing a large HEC-RAS model within a single AutoCAD drawing.4. click River tab > Create Reach Data panel > Junctions.

the dialog box will change to allow you to define the necessary data. Name Defines the unique name of the junction being created. then comparing the computed energy grade lines for the cross sections just downstream of the junction.1. Flow optimizations at junctions are performed by computing the water surface profiles for all of the reaches. This methodology continues until an energy balance is reached. Junction Type Specifies either Confluence or Split as the type of junction being modeled.1 Illustration of different junction types supported
Optimize Diversion Split Flow Informs the HEC-RAS software to determine the amount of flow that splits. Computation Mode Specifies either Energy or Momentum as the computation method to be used at a confluence junction. If the energy in all the reaches below a junction is not within a specified tolerance (0. then the flow going to each reach is redistributed and the profiles are recalculated. Based upon the junction type selected.
. Up to 16 characters can be used in the junction name. The software continues to attempt to balance the flow split until the energy grade lines of the receiving reaches are within the specified split flow tolerance.
Figure 2. at a junction where the flow splits into two separate downstream receiving reaches.Using the Program
2-9
junction. and is unavailable (grayed out) for confluence junctions. The dialog box entries that define a junction are described below. This entry is only available for split flow junctions.02 foot). To delete an existing junction. select the junction to be deleted from the list of junctions and then click Delete.4.

. this section becomes a single drop down list that allows you to select the upstream reach. this section becomes a table and multiple upstream reaches can be defined as combining at the junction. In most cases the amount of energy loss due to the angle of the tributary flow is not significant. The energy equation does not take into account the angle of a tributary coming in or leaving. a drop down list shows a list of available reaches.2 Junction flow angle
Description Allows you to include a description of the junction being defined. the angle should be left blank or set to zero. there are situations where the angle of the tributary can cause significant energy losses. In these situations it would be more appropriate to use the momentum approach. The default is to have the weight force turned off. Downstream Reach(es) When defining a confluence junction. Also. Upstream Reach(es) When defining a confluence junction. The Angle column is used to enter an angle for any river reach that is coming into or exiting the main river. an Angle column is added to the table next to the Length column.
Figure 2. When defining a split flow junction. and using the energy equation to model the junction is more than adequate. For the reaches that are considered to be the main river. while the momentum equation does.1. this section becomes a single drop down list that allows you to select the downstream reach. When the momentum approach is selected.4. For each row within the table. you have the option to turn friction and weight forces on or off during the momentum calculations. However.2-10
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
In HEC-RAS a junction can be modeled by either the energy equation or the momentum equation.

When starting out with a new or existing drawing.4. this section becomes a table and two downstream reaches can be defined as splitting at the junction. Length(s) The Junction dialog box defines the reach lengths across the junction. This ID marker can be moved. However. you do not need to define or manage the river reach since the software will automatically set up and manage this initial river reach. This allows for the lengths across very complicated confluences (or flow splits) to be accommodated.
.2
Adding a New River Reach
The software internally forces all HEC-RAS entity data to be assigned to a river reach. For each row within the table. For the upstream reach(es). a drop down list shows a list of available reaches. if it is necessary to define another river reach in the same drawing. if required. when multiple river reaches must co-exist within the same AutoCAD drawing. the flow distance entry defined at the next upstream cross section should be left blank or set to zero. the software assigns a river reach to the drawing. However.
Figure 2. All modeling data entered into the drawing is then attached to this river reach. When the first River Analysis command is launched. the software will locate the river reach ID marker adjacent to the cross section. the software automatically assigns a river reach to the drawing.3 Junction flow lengths
2. rather than at the next upstream cross section description. If only one model (or river reach) is to exist in the drawing.1. then a new river reach must be assigned. All modeling data entered into the drawing is then assigned to this river reach.4. you should understand river reaches and be aware which river reach is currently active.Using the Program
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When defining a split flow junction. When the first cross section is defined in the model.

2. However. If additional cross sections are added downstream of this cross section.4. Therefore. If the cross section is cut from a topographical map. As soon as the first cross section is added to a new river reach. or click River tab > Input panel > Section Description to make the cross section IDs different in the current and destination river reaches. The current reach name is shown in the reach drop-down on the River tab > Create Reach Data panel. such as when a skeletonized river model is broken down into a more detailed model as additional. Any new cross section data entered is assigned to this river reach. the river reach ID marker is positioned adjacent to the topographical map cross section. click River tab > Create Reach Data panel > Reaches dropdown > Reassign Section. click River tab > Create Reach Data panel > Reaches drop-down > Create Reach. the river reach identifier is automatically repositioned next to the most downstream cross section.3
Reassigning Cross Sections
Each cross section must belong to a single river reach. The Create Reach dialog box allows you to assign a unique ID (positive integer from 1 to 100) to the river reach.
Reassigning Multiple Cross Sections
The Reassign Cross Section dialog box enables you to select more than one cross section in the cross section.
. for large dendritic river models. To reassign a river reach. if the river reach identifier is manually repositioned (see the section titled Moving the River Reach ID Marker on page 2-13).
Cross Sections ID Collisions
When reassigning cross sections. the river reach ID marker is positioned next to the cross section grid. the river reach ID marker is displayed next to the cross section. it is necessary to insert two cross sections adjacent to each other—one at the end of one reach and the other at the start of the next. you cannot transfer cross sections for which an identical cross section ID already exists in the destination river reach. you must either delete the matching cross sections from the destination river reach. To reassign these cross sections. it is then no longer automatically repositioned. you can reassign cross sections from the current river reach to a different river reach. where long river reaches have to be broken into two or more separate models. the software creates a new river reach and makes it current. It may be necessary to reassign cross sections to a different river reach. The combination of the river name and reach name must be unique. it cannot belong to multiple river reaches. This allows continued modeling of the water surface profile between the specified river reaches.2-12
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
To add a new river reach to the drawing. along with defining a River name and Reach name. Otherwise. smaller side reaches are added. In the Reassign Cross Section dialog box. When you click OK.

although it can be located anywhere on the drawing.4.e. etc. Once the river reach identifier is manually moved.e. click River tab > Create Reach Data panel > Reaches drop-down > Delete Reach. it makes sense to locate the river reach identifier near the downstream cross section.
Deleting the River Reach Identifier
If you accidentally delete the river reach identifier. The View Reach Extents dialog box enables you to specify which reach to view on the drawing.4. To move the river reach ID marker. river name. If additional cross sections are added downstream of this cross section. the river reach identifier's position is no longer automatically updated. If cross sections have been cut from a topographical map.4.5
Editing a River Reach
To edit the ID. starting water surface elevation. the river reach identifier is automatically repositioned next to the most downstream cross section. or reach name of an existing river reach.6
Moving the River Reach ID Marker
When a cross section is first added to a river reach. and click OK. etc.7
Selecting a River Reach
Select a river reach from the list on the River tab > Create Reach Data panel. However. the river reach identifier can be manually moved about the drawing. select the appropriate river reach to delete. In the Delete Reach dialog box.
2. discharge.4. it is positioned next to the cross section grid. the river reach ID marker is positioned adjacent to the topographical map cross section.) from the drawing.4
Deleting a River Reach
To delete a river reach and its associated data (i. select it and use the grip to move it.
2.) are defined. Otherwise.4. If the cross section was cut from a topographical map.. the software will display the extents of the cross section data associated with the selected river reach on
..Using the Program
2-13
2.
Recommendation
It is recommended that the river reach identifier be located adjacent to the most downstream cross section. click River tab > Navigate panel > Zoom to Reach Extents.
2. where the water surface boundary conditions (i. the software positions the river reach ID marker next to the cross section. Since most water surface profile models are subcritical. click River tab > Create Reach Data panel > Reaches drop-down > Edit Reach. cross sections. the software will later re-create it— if required.8
Zooming to a River Reach
To zoom to the extents of a river reach.
2. if desired.

1
Creating a Cross Section View
Before you can describe a cross section's location.
2. this section provides additional information for management of the cross section views. such as the cross section geometry. etc. roughness values. Cross section views can be moved about the drawing at any time without affecting the cross section entity information.
2. Otherwise. Deleting a cross section view deletes the cross section entity from the drawing.5
Cross Section Views
When creating cross sections.5.
Figure 2. you need to assign a cross section ID using the Create Section dialog box. and related information. the software will display the most downstream cross section.2-14
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
the topographical map. bank stations. However.1 Typical cross section view
A cross section view displays all of the cross section related entity information. Note that all of the methods provided within the software for extracting ground geometry from a topographical map and the provided methods for importing ground
.5. if there is no topographical map data associated with the selected river reach. geometry. the software will automatically manage the creation and editing of cross section views. ineffective flow areas. This dialog box is reached by entering RMS_XSAdd on the command line.

Description (optional) This entry is used for entering an option description of the cross section. Station Axis: Leftmost Station Defines the starting station (in feet or meters) of the cross section view horizontal station axis. This entry can be positive or negative. The software will then regenerate the cross section views at the revised scaling factors. Unique IDs must be ascending in value. This entry must be positive and be no more than six characters long.
Cross Section View Scaling Factors
All of the cross section views generated by the software use the same scaling factors for the elevation and stationing axes. This entry is the only information required for this dialog box to add a new cross section grid.
. You can accept this number or change it. see the section titled Configure Cross Section Views on page 2-81. from downstream to upstream. For more information on how to adjust the scaling factors. This length is added to the starting elevation to determine the ending (highest) elevation of the cross section view vertical axis. The cross section view horizontal axis begins at this station value. The cross section view vertical axis begins at this elevation value.Using the Program
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geometry automatically display the Create Section dialog box. this command is not often used. No two cross sections within the same river reach may have the same cross section ID. This length is added to the starting (leftmost) station to determine the ending (rightmost) station of the cross section view horizontal axis. Unique ID Specifies a unique number to identify the cross section. you can. Therefore. This entry must be positive. This entry must be positive. specify the following parameters. This is how the software is able to maintain the numerical placement of the current cross section relative to all the other specified cross sections. The Create Section dialog box initially presents a unique ID number for the new cross section view. In the Create Section dialog box. revise these scaling factors. This entry must be positive. Elevation Axis: Axis Height Defines the length (in feet or meters) of the cross section view vertical elevation axis. However. all other data entries will default to the values of the currently active cross section grid. Station Axis: Axis Length Defines the length (in feet or meters) of the cross section view horizontal station axis. Elevation Axis: Starting Elevation Defines the starting (lowest) elevation (in feet or meters) of the cross section view vertical elevation axis.

Using the AutoCAD MOVE command. caution must be exercised when deleting a cross section view since all of its associated entity data will also be deleted. one can simply define the cross section at the downstream face of the bridge and then copy this cross section to the upstream face of the bridge.4
Editing a Cross Section View
The Edit Section dialog box allows you to edit the currently active cross section's grid attributes.
Caution When Copying a Cross Section View
When copying an existing cross section view to a new cross section location. when defining a bridge.5. the downstream and upstream face cross sections of the bridge structure are very similar. etc. click River tab > Input panel > Section Geometry drop-down > Copy Section. titled Editing a Cross Section Grid).2-16
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
2. The currently active cross section view is automatically selected. profile adjustments. split flow descriptions. the overbank and channel flow lengths must be re-specified for both the initial cross section grid and the copied cross section view(s) to account for their actual flow lengths. Rather than defining each of these cross sections separately. You should first consider whether it would be more advantageous to simply edit the cross section view (see the next section. it is easy to select the cross section ground geometry and bank stations and then displace the selected entities up or down by the required amount. In the Copy Section dialog box.
. specify the ID of the new cross section view for the current cross section view and related data to be copied. some of this associated data must be altered after copying. Associated data includes bank stationing.5.2
Copying a Cross Section View
Many times it is useful to simply copy an existing cross section view and its related cross sectional geometry to another cross section location. floodplain encroachments. the cross section view's associated data will also be copied. However. Therefore.
2. the cross section's ground geometry must be raised or lowered by a fixed amount. In the Delete Section dialog box.
2. click River tab > Input panel > Section Geometry drop-down > Delete Section. For example. For example.
Caution When Deleting a Cross Section View
The cross section view entity stores the cross section associated entity information.
Ground Geometry Elevation Adjustment
Many times. To copy the current cross section view and all of its associated data to a new cross section location.3
Deleting a Cross Section View
To delete a cross section view and all of its associated data. select the appropriate cross section view(s) to delete. when a cross section view is copied to an adjacent location.5. bridge and culvert descriptions. Multiple cross sections can be deleted. flow lengths.

For example.6. select the cross section to make current. such as the cross section expansion and contraction values. if the model is defined in US units. enter RMS_XSEdit on the command line. channel. as defined in the Cross Section Description dialog box.5.Using the Program
2-17
To edit the current cross section view’s attributes. Channel Reach Length: Causes the cross section ID renumbering to be based upon the distance defined for the Channel Reach Length entry. To select a cross section. For example.5.
.
•
•
Increment Unit Defines the unit of measure to be used in the cross section renumbering when using the reach length options. The currently active cross section is identified in the cross section list on the River tab > Input panel. The data entries for the Edit Section dialog box are identical to those described in the section titled Creating a Cross Section View on page 2-14. or meters or kilometers. • Fixed: Define a fixed increment to be used in the cross section ID renumbering. Cross Section ID Increment Specify how cross section IDs are to be incremented.5
Renumbering Cross Sections
If it becomes necessary to renumber all the cross sections in the current river reach. and right reach length data entries.
2. click River tab > Input panel > Section Geometry drop-down > Renumber Section. Average Reach Length: Causes the cross section ID renumbering to be based upon the average reach length distance defined for the left. beginning at the starting cross section ID. In the Renumber Section dialog box. on the command line. entering a value of 100 causes the IDs to be renumbered in 100 increments. as defined in the Cross Section Description dialog box.5. the cross section must be currently active.
2. The Edit Section dialog box can be used to manually resize the cross section view to fit the extents of cross section related data (such as ground geometry. specify the following parameters: Starting Cross Section ID Specify a new starting ID for the most downstream cross section. then the cross section ID increment can be based upon either feet or miles.6
Selecting and Viewing Cross Sections
There are several ways to select and view cross sections. and ineffective flow areas). enter RMS_XSSelect. roadway geometry.1 Selecting a Cross Section
To define specific information about a cross section.
2. Only one cross section can be active at any given time. In the Select Cross Section Grid dialog box.

enter RMS_XSResize. To automatically resize the all cross section views.
2. or deleting a cross section's ground geometry.
2.6. click River tab > Navigate panel > Zoom to Section Surface.5 Viewing Previous and Next Cross Section Views
To view the previous cross section grid. it may be desirable to resize the cross section view to fit the extents of this data. click River tab > Input panel > Section Geometry drop-down > Resize Section views. Selecting a cross section grid from the Zoom to Section View dialog box displays the selected cross section grid in the current viewport and makes the selected cross section grid currently active. then this display will be maintained.5.
2.6.6.
. and energy grade line.
2.
2. on the command line.2-18
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
If you are currently looking at a different cross section or a topographical map view. select the section view and click OK.3 Viewing a Cross Section on a Surface
To view the current cross section on the surface it is sampling. roadway geometry. In the Zoom to Section View dialog box.7
Resizing a Cross Section View
After adding. editing. its ID is displayed in the cross section list on the River tab > Input panel.5. its ID is displayed in the cross section list on the River tab > Input panel.5.5. Instead of manually resizing the currently active cross section grid using the Edit Cross Section Grid dialog box. on the command line. or ineffective flow area data.4 Viewing Cross Section Analysis Results
The cross section grid can display the computed water surface.6.2 Zooming to a Cross Section
To zoom to a cross section view. To view the next cross section grid.5. on the command line. See the section titled Displaying Cross Section Results on page 2-50 for information on how to specify what analysis results are to be displayed on the specified cross section grids. critical water surface. When a cross section has been made current. enter RMS_XSPrev. the software can automatically resize the view to the extents of the cross section related data. To automatically resize the current cross section view. enter RMS_XSNext. click River tab > Navigate panel > Zoom to Section View. When a cross section has been made current.

6. This allows you to select only the contours where the cross section cutting line direction changes.Y coordinates on the surface. you can transparently pan and zoom to quickly move about the surface during the digitizing process.
4. it is not necessary to pick every contour in a cross section. Choose a representative cross section that best describes the flow characteristics of the reach being modeled.1
Cutting Sections from a 3D Surface
The 3D map cross section geometry input method is the fastest and most powerful method of digitizing a cross section. no matter how the ground points are input. Refer to the section titled Configure Cross Section Views on page 2-81 for more information. This method allows you to cut a cross section directly from an on-screen 3D topographical contour map or 3D TIN (triangulated irregular network). However. in sequence (leftmost station to rightmost station). A 3D topographical map differs from a 2D topographical map. Cut a cross section from the surface by picking cross section ground station points. Click River tab > Input panel > Create Section drop-down > 3D Section Cut. You may not want elevation data to be read from particular AutoCAD layers—the Configure Elevation Layers dialog box is provided for this purpose. You can also explicitly specify each cross section ground station's X.Using the Program
2-19
The Configure Section Views dialog box provides settings that control how views will be resized. In the 3D Section Cut dialog box. specify the Leftmost (starting) ground station. 2. Although it’s best to display the desired view of the surface before beginning this method. as discussed in the section titled Editing Cross Section Geometry on page 2-24. be aware that the elevation is always taken from the nearest 3D contour. The starting station can be any arbitrary value. Under Initial Values. 3. enter a Unique Cross Section Grid ID. You cannot directly define the elevation of a digitized ground point.
.
Because the software reads elevations from any contours crossed by the cutting line. in that it has elevation data associated with the displayed contour lines or points. which correspond to contours.
2. but can later redefine the elevation (or station) using the Edit Geometry input method. See the section titled Configure Elevation Sources on page 2-84 for more information.
2.6
Defining Cross Section Geometry
Autodesk River Analysis provides a variety of tools for automatically and manually inputting cross section ground geometry. To cut sections from a 3D surface: 1.

Cut a cross section from the surface by picking cross section ground station points which correspond to contours. simply click the 3D point.6. in sequence (leftmost station to rightmost station). you can use 3D points at elevations when cutting a cross section. because the software will interpolate elevations (using the surface contour interval) from any contours crossed by the cutting line. lines. 2. This technique will help when cutting a cross section using points at elevation. A problem associated with using points at elevation when cutting a cross section is that the points may not lie along a path where you can cut a cross section. If an entity is found on a layer whose status has not previously been defined. Any points. Rather than selecting a point on a contour.
It is not necessary to pick every contour in a cross section.
4.2
Cutting Sections from a 2D Surface
This cross section geometry input method allows you to cut a cross section from an onscreen 2D surface. To cut sections from a 2D surface: 1. See the section titled Configure Elevation Sources on page 2-84 for more information. Click River tab > Input panel > Create Section drop-down > 2D Section Cut. specify the Leftmost (starting) ground station. Using the standard AutoCAD LINE or 3DPOLY command along with the NODE OSNAP option. you may want to connect lines between the 3D points. You may not want elevation data to be read from particular AutoCAD layers—the Configure Elevation Layers dialog box is provided for this purpose. polylines. This allows you to select only the minimum and maximum contours as the cross section is being cut. Under Initial Values. In this situation. enter a Unique Cross Section Grid ID. you will be prompted to configure the layer's status. you can connect a 3D line between existing 3D points. the software will search for any elevation data on the surface that intersect the drawn cross section line. or where the cross section cutting line direction changes. In the 2D Section Cut dialog box. but only for layers that have been configured as valid elevation layers. 3.2-20
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Using Points at Elevation
If desired. which has no elevation data associated with the displayed contour lines. The starting station can be any arbitrary value. or TIN polyfaces intersected will be examined for possible elevation data.
Verifying Elevation Layers
When entering cross section ground geometry using the 3D Section Cut or 2D Section Cut commands.
2.
.

A raster topographical map has no elevation data associated with the displayed contour lines.1650. In the Section Cut by Object dialog box. to specify the layers and surfaces from which elevation data is extracted. Enter in a new elevation (a single number. When cutting the cross section from the raster topographical map. in sequence (leftmost station to rightmost station) on the screen topographical map.
Although it’s best to display the desired view of the surface before beginning this method. with no spaces). To cut a section from a polyline: 1.
. pick the cross section ground station points that correspond to raster contour lines. This method can be automated using the Automated Section Cut command. Under Trace Line Options.
2. Click River tab > Input panel > Create Section drop-down > Section Cut by Object.
Click OK.Y coordinates have been entered (such as 7410. Trace Line and Use Line’s Elevation Data: Select this option to use the elevation data that is assigned to a 3D polyline. such as 1650).Using the Program
2-21
The current digitizing elevation is displayed on the Command line and may be changed while digitizing cross section ground stations by one of the following methods: • • • Press the Up and Down cursor keys will increase or decrease the digitizing elevation by the current step value.
• 3.
2. and then click Configure Elevation Data. specify where the elevation data is sampled: • Trace Line as a Cutline and Use Elevation Layer Data: Select this option.6. enter a Unique Cross Section ID. 4. The software will then follow along the polyline and extract the cross section geometry.3
Cutting a Section from a Polyline
The Section Cut by Object command allows you to extract cross section geometry from a polyline on a surface. Enter the new elevation as the third coordinate after the cross section ground station's X.420. you can transparently pan and zoom to quickly move about the surface during the digitizing process. Select the left side (looking in a downstream direction) of the polyline.
Digitizing from Screen Raster Maps
This cross section geometry input method also allows you to create a cross section by drawing it from an on-screen raster topographical map. This enables you to adjust the polyline to the desired position before the cross section is extracted.

navigate to the file to import. or create a completely new cross section.
. which allows you to control the extent of the ground geometry to import. specify a Unique Cross Section ID. create a replacement cross section. If the selected data file is a HEC-RAS geometry file or HEC-2 input card file. this method allows you to insert the imported ground geometry data into the currently active cross section. you can specify restrictions to limit which ground stations are to be imported. In the Import Section Geometry from File dialog box.2-22
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
2.
3.4
Creating Sections from Imported Data
The Import Section Geometry from File command allows you to import all or only a portion of the ground geometry for a cross section from a number of file types: • • • • HEC-RAS geometry file HEC-2 input card file XYZ or YXZ (Northing-Easting) coordinate data file a station/elevation or elevation/station point file
This method provides greater accuracy in specifying the cross section ground geometry by allowing you to insert surveyed data directly into the model. the software automatically determines the file type.
XYZ and YXZ Coordinate Data File Format
In order for the software to be able to identify that the file being imported is an XYZ or YXZ coordinate data file. Note that an YXZ coordinate data file is more commonly referred to as a northing-easting-elevation coordinate file. Click OK. To create sections from imported data: 1. Click River tab > Input panel > Create Section drop-down > Import Section Geometry from File. this dialog box allows you to specify the cross section from which to import ground geometry. If the selected data file is an XYZ or YXZ coordinate data file.6.
4. or a station/elevation or elevation/station point file. In the New Section Grid dialog box. Click OK.
2. The software then displays the Import from File dialog box.
After selecting the data file to import. the file must be properly formatted. You can also specify restrictions to limit which ground stations are to be imported. As with other ground input methods.

Y.0 is assumed. Starting with the fourth line. If this line is left blank. X. Each ground point's Z coordinate value is added to the specified elevation datum adjustment value to determine the resulting elevation.4.1 Surveyed ground points do not need to lie along a straight line.0 is assumed. The starting horizontal station value cannot be negative. However.
The software uses the Pythagorean Theorem to determine the absolute distance between adjacent ground point stations using the specified X and Y coordinate values. The third line defines an elevation datum adjustment value. This distance is accumulated. This adjustment value allows you to adjust the elevation of the coordinate data.
2. The following figure illustrates that the surveyed ground points do not need to reside along a straight line.
5.Using the Program
2-23
Follow these guidelines when developing a coordinate data file: 1.6. Spaces.
Figure 2. being added to the specified starting horizontal station value to determine each ground point's resultant stationing value. each remaining line in the file corresponds to the X. but should form a line perpendicular to the stream flow
. commas.
4. The second line defines the starting horizontal station value. If this line is left blank. The first line in the coordinate data file must contain the keyword XYZ (or YXZ) by itself. and Z coordinates) of a single 3D ground point. an elevation adjustment of 0. and/or tabs can be used to delimit the coordinate values of a point. Negative and positive coordinate values are allowed. and Z coordinates (or Y. a starting horizontal station of 0. these surveyed points should form a line perpendicular to the stream flow.
3.

each remaining line in the file corresponds to the station and elevation (or elevation and station) of a single ground point. See the section titled Creating Sections from Imported Data on page 2-22 for more information. and/or tabs can be used to delimit the station and elevation values of a point. and delete individual ground points for the current cross section grid.
4. From this dialog box you may also import cross section ground points from an existing HEC-RAS geometry file. which allows the cross sectional data to reside within a single file. Spaces. or an XYZ coordinate data file. a starting horizontal station of 0.
2. a station/elevation point file. edit.6. To edit cross section geometry: 1. edit. Follow these guidelines when developing a point file: 1. In addition. This adjustment value allows you to adjust the elevation of the stored data. The second line defines the starting horizontal station value. If this line is left blank. The starting horizontal station value cannot be negative. an elevation adjustment of 0. HEC-2 input card file. the file must be properly formatted in order for the software to be able to identify the file being imported as a station/ elevation and elevation/station point file. and delete horizontal roughness. Click River tab > Input panel > Section Geometry drop-down > Section Geometry Editor. Negative stationing values are not allowed. The third line defines an elevation datum adjustment value. The first line in the station/elevation point file must contain the keyword XY (or YX) by itself.0 is assumed. If this line is left blank. add. and roadway elevation values. Starting with the fourth line. The Section Geometry Editor dialog box can be used to insert.0 is assumed.
. The file format of a point file is very similar to that of an coordinate data file.
5.
3. you can insert. Each stationing value is added to the specified starting horizontal station value to determine each ground point's resultant stationing value.2-24
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Station/Elevation and Elevation/Station Point File Format
As with the XYZ and YXZ coordinate data file.
2. Each ground point's elevation value is added to the specified elevation datum adjustment value to determine the resulting elevation.5
Editing Cross Section Geometry
Many times it is convenient to directly edit the cross section geometry station and elevation values once they have been input by one of the previously described input methods. low chord elevation. commas.
Importing Multiple Cross Sections
The software provides a separate import method in order to import data for multiple cross sections.

Left Station. To graphically select a station to edit. and Right Station data entries to their default values. click New File. click Import.
Importing Ground Geometry Data
To import ground geometry from a HEC-RAS geometry file. Left Station. In the Merge Geometry Data dialog box. you can select the file from which to import data. Restrictions to limit which ground stations are to be imported can be specified. If the selected data file is a HEC-RAS geometry file or HEC-2 input card file. click cells and enter data to modify the cross section geometry: > > > Click < to graphically select a horizontal station or elevation from the cross section grid. this dialog box allows you to specify the cross section from which to import ground geometry. Elevation Offset. you can select whether to replace the old station points with the new imported station points. From the Import Section Geometry from File dialog box. Both values default to zero when the dialog box is first displayed.
In the Section Geometry Editor dialog box. or an XYZ coordinate data file. enter new station limits in the edit boxes or simply pick the desired starting or ending station from the Preview image. In the Cross Section Data table.
In the Cross Section Data table. a station/elevation point file. To select a different data file from which to import ground geometry. if ground geometry already exists in the current cross section. To change the Left Station and Right Station values. specify the Reach and Cross Section.
. After selecting the data file to import. click Pick. and Right Station data entries return to their default values whenever a cross section is selected from the list. To insert a new station and elevation.
3. Note the radio buttons in front of the Left Station and Right Station edit boxes.Using the Program
2-25
2. Note that the Station Offset. the software automatically determines the file type. Station and/or elevation offset values to adjust the position of the ground geometry can also be defined. the two green colored rows correspond to the left and right overbank stations. Click 0 to reset the Station Offset. After selecting the data file to import. this setting determines which edit box will be adjusted by picking a cross section station from the Preview image. HEC-2 input card file. Elevation Offset. click New. the software displays the Merge Geometry Data dialog box.

If any other reference point type is specified. The Type list specifies the reference point that is to be used in determining how much to shift the stationing. However.6. Add Constant Elevation Allows you to add a constant elevation amount to all of the cross section ground geometry elevation values. The Adjust Section Geometry dialog box contains the following controls: Add Constant Station Allows you to add a constant station amount to all of the cross section ground geometry station values.6
Adjusting Cross Section Geometry
You can adjust the geometry of a cross section. then a new Target station must be defined. To adjust the current cross section geometry: Click River tab > Input panel > Section Geometry drop-down > Adjust Section Geometry. See the section titled Reducing Cross Section Points on page 2-27 for more information. Click Pick to graphically select the elevation amount from the current cross section. HEC-RAS as an upper limit of 500 ground points per cross section. the Reduce Section Points command can be used to weed redundant ground points from the cross section.000 ground points per cross section. Click Pick to graphically select the station amount from the current cross section. Shift Stationing Allows you to shift the stationing to the left or right by a specified amount.2-26
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Maximum Number of Ground Points
The Section Geometry Editor dialog box supports a maximum of 5. The following reference point types are available: • • • • • • • Custom Thalwag Centerline Centered Between Banks Left Bank Right Bank Leftmost Station Rightmost Station
If the Custom reference point type is selected. If the cross section being defined has more than the model’s upper limit.
.
2. then an existing Source station and new Target station must be defined.

By default. Similarly. the HEC-RAS analysis engine that is supplied with the software can handle 500 points per cross section. Automatically Resize Cross Section Grid Automatically resizes the cross section grid after the specified cross section geometry adjustment has been applied. a factor of 0. to expand the distance between stations by 20%. Reverse Ground Stationing Order Reverses the order of the cross section stationing. For example.7
Reducing Cross Section Points
The software allows you to specify up to 5. However.6. The new ground point’s elevation will be interpolated from the adjacent ground points. Similarly.2 should be specified.2 should be specified.2 should be specified.Using the Program
2-27
Select Create New Station to cause a new ground station to be created.5 should be specified.. Left Overbank Factor Allows you to specify a factor to be multiplied to the left overbank ground geometry station spacing to either shrink or expand the left overbank area. Note that the leftmost starting station is used as a fixed reference point for scaling the ground geometry stationing. In addition.000 points per cross section. Channel Factor Allows you to specify a factor to be multiplied to the channel ground geometry station spacing to either shrink or expand the channel area. a factor of 1. Note that the leftmost starting station is used as a fixed reference point for scaling the ground geometry stationing.
2. to expand the distance between stations by 20%. to shrink the distance between ground stations in the left overbank area by 50%.
.5 should be specified. if Centered Between Banks is specified as the reference point type will cause a new ground point to be created if a centerline station does not already exist. Adjustment Extent Allows you to control the extent of the specified cross section geometry adjustment. a factor of 0. if necessary. Right Overbank Factor Allows you to specify a factor to be multiplied to the right overbank ground geometry station spacing to either shrink or expand the right overbank area. For example. For example. a factor of 1. right to left) and the cross section stationing needs to flip. By default. For example. a factor of 0. to expand the distance between stations by 20%. only the current cross section is adjusted. Similarly. the specified adjustment can be applied to the entire river reach or all defined river reaches.e. this option is selected. to shrink the distance between ground stations in the right overbank area by 50%. a factor of 1. end for end.5 should be specified. This is useful in situations where the cross section geometry was cut from a surface in the wrong direction (i. Note that the leftmost starting station is used as a fixed reference point for scaling the ground geometry stationing. to shrink the distance between ground stations in the channel by 50%.

e. points outside the bank stations).
Reduction Rules
The software allows you to select FEMA (Federal Emergency Management Agency) rules to use in reducing the number of ground points for a cross section.e. Those points with the least area which fall within the specified reduction rules are removed to meet the specified number of points allowed. the software automatically eliminates those points which add the least resolution to the existing ground geometry. The software does not add ground points if the original geometry violates these rules. allowing you to check the software's computed ground point reduction. When satisfied with the revised geometry.. Allow a maximum horizontal spacing of 10% of the main channel width between channel ground points (i. Note that the software only applies the maximum spacing requirement rules to reduce the total number of ground points. click OK. These rules include the following: • • • • Allow a maximum of 90 ground points. it may be necessary to reduce the number of cross section points to this limit. flood overbank stations. ground points that define starting and ending stations.
The software uses a triangular area comparison algorithm to determine each point's degree of ground geometry resolution. However. Click No Rules to clear the above rules.
Click FEMA Rules to select all of the above reduction rules. It then computes the triangular area formed by these three points and stores this area with the point. You can also select individual reduction rules to be applied.
3. Allow a maximum horizontal spacing of 5% of the total cross section width between floodplain ground points (i. The Reduce Section Points dialog box displays the existing ground geometry and the total number of points defined for the current cross section. and roadway geometry stations are not removed.2-28
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
When attempting to perform a HEC-RAS simulation. points inside the bank stations). bridge low chord geometry stations. If so. click Preview. Points that define significant breaks in the cross section geometry are allowed to remain. horizontal roughness stations. Allow a maximum vertical spacing of 20% of the total cross section height between ground points.
.
4. The software does this by looking at each point and its two adjacent points..
2. By specifying the number of points allowed. The software will then display the revised cross section ground geometry along with the original ground geometry. the software will warn you if the number of specified cross section points are over the allowable limit. After specifying which reduction rules to apply and the total number of cross section points allowed. To reduce the number of cross section points: 1. Click River tab > Input panel > Section Geometry drop-down > Reduce Section points.

draw a temporary cross section cut line that represents where the ground geometry for the selected cross section grid should be placed. sometimes linking an existing cross section to a surface is a trial and error process—especially when the exact location of the original cross section is not known. and finally end with the rightmost station. the software will automatically draw cross section labels and related data. you may import a HEC-2 card file into a new drawing containing a surface of the region being studied. When the data is imported. To link an existing cross section view to a surface: 1.e.
2. This also allows the computed water surface profile to be displayed on the surface. Not every ground station point needs to be identified—only identify the starting and ending stations and where the cross section cut changes direction. Select a cross section view to link to the surface (see the section titled Selecting a Cross Section on page 2-17). As the cross section views become linked to the surface. After using the Trace Section Location command. etc. on the surface. the software automatically links the cross section view and related information (i. If the bank stations do not appear to correctly align with the topographical map channel banks. such as bank stations.6. then the cross section cut line will need to be moved upstream. or from side-to-side in an attempt to correctly locate it.
2. it may be necessary to link cross section views (and related information) to the surface in situations where no linkage exists. Click River tab > Input panel > Link Section drop-down > Trace Section Location.
3. ground geometry. bank stations.
.Using the Program
2-29
2. For example. You can manually assign linkages between the imported ground geometry (cross section views) and cross section cut lines drawn on the surface. This procedure can be repeated for each cross section view that needs to be linked to the surface. After you have drawn the cut line on the surface.. However. This enables you to edit the cross section related information from either the cross section view or the surface by simply clicking on the representative graphic entity. there is no link between the imported cross section ground geometry and the surface geometry.) to a cross section cut line shown on the Civil 3D surface. Start with the leftmost station.8
Tracing a Cross Section Cut Line on a Surface
When using the 3D and 2D section cut commands. you are generally able to tell if the cross section does not belong where it was drawn by looking at where the cross section bank stations lie on surface. include station locations where the cross section cut changes direction. downstream. If the linked cross section line is not laid out to your liking. On the surface.6.9
Moving a Cross Section Cut Line
When using the Trace Section Location command. as presented in the section titled Tracing a Cross Section Cut Line on a Surface. the software will replace this line with a new line containing all the points that describe the ground geometry for the cross section view. this command can be repeated and the cross section cut line redrawn.

6.
2.6. pick the new cross section rotation angle. Click OK.11
Recutting a Cross Section
Sometimes it is necessary to recut an existing topographical map cross section. In the Rotate Section Location dialog box. The software allows you to recut previously cut cross sections. see the section titled Recutting a Cross Section on page 2-30. such as when new topographical geometry data is imported into the drawing file. 3. specify the reference point to use. specify the reference point to use. The Move Section Location command can be used as many times as necessary to precisely locate the cross section cut line. In the drawing.
2. see the section titled Recutting a Cross Section on page 2-30. Click River tab > Input panel > Link Section drop-down > Move Section Location. you may have to rotate the cross section on the surface in an attempt to correctly locate it.
2. 4. pick the new reference point location on the surface. the original ground geometry is maintained. perhaps both existing and proposed contour line data is in the same file. Click OK. in order to update the cross section ground geometry. For example. on separate layers. To rotate a cross section cut line: 1. In the drawing. If it is desired to recut the ground geometry at the new cross section location.
This command does not alter the original cross section ground geometry. generating new cross section geometry.
This command does not alter the original cross section ground geometry.
2. The Rotate Section Location command can be used as many times as necessary to precisely locate the cross section cut line.10
Rotating a Cross Section Cut Line
After using Trace Section Location and Move Section Location commands (as presented previously in section titled Tracing a Cross Section Cut Line on a Surface on page 2-29 and the section titled Moving a Cross Section Cut Line on page 2-29). In the Move Section Location dialog box. If it is desired to recut the ground geometry at the new cross section location.2-30
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
To move a cross section cut line: 1. 3. Click River tab > Input panel > Link Section drop-down > Rotate Section Location. To recut a cross section:
. 4.

see the section titled Graphical Editing using Grips on page 2-41.
3. pick the ground line to move an individual ground point shown on either the cross section view or surface.Using the Program
2-31
1. pick the ground line. or all cross sections in the current river reach. and press Enter (or the right mouse button) to toggle into Move mode. AutoCAD automatically highlights all the ground points. press Esc twice. To change the elevation of an entire ground line on a cross section view. then the topographical map water surface results could possibly be inaccurate.
Defining Elevation Layers
The software will read elevation data from the defined elevation layers that contain ground terrain information. This will display the Configure Elevation Layers dialog box (see the section titled Configure Elevation Sources on page 2-84). Click OK.
2. while at the AutoCAD command line. select any point on the line.
• •
For more information on AutoCAD grips. Then drag the entire ground line to the desired elevation on the view. Moving a cross section cut line on the surface will automatically move the related bank stations and connecting lines. This method can also be used to adjust the position of a cross section cut line drawn on the surface. Editing a topographical map cross section cut line using grips automatically updates the ground geometry shown on the cross section grid. There are a few things to be aware of when using grips to edit ground geometry: • • Changing a ground point's location on the cross section view automatically updates the corresponding ground point on the surface (or vice versa). To clear grips from the selected ground line. For example.12
Graphical Adjustment of Ground Geometry
The software allows you to perform ground geometry adjustments graphically using AutoCAD grips. 2. allowing you to select what layers are to be used for reading elevation data.
Click River tab > Input panel > Create Section drop-down > Recut Section.6. River Analysis entities are not dynamically updated. NOTE: Related River Analysis entities are dynamically updated only when they are edited within the River Analysis commands. To change which layers are to be read for elevation data. Since the software uses the geometry shown on the cross section view when performing its water surface profile calculations. select Configure Layers from the Recut Existing Cross Sections dialog box. Pick the ground point you want to move and drag it to its new location.
. select whether to recut the current cross section. When AutoCAD commands (such as MOVE) are used. In the Recut Section Points dialog box. if this geometry data does not correspond to the underlying digital terrain map.

Click Pick to interactively select the downstream end of the river centerline alignment polyline. when cutting cross section along a irrigation canal. Multiple Cutlines Enables you to draw 2D polylines on the surface to define where to extract cross section geometry—prior to actually extracting the cross sections. the extracted cross sections will be the same. Be assigning a template cutline.7. the software automatically extracts the river cross section geometry from topographical map. The following methods are provided: Perpendicular Extracts the cross sections from the river topographical data perpendicular to the previously drawn river centerline alignment. Cross Section Cutting Method The cross section cutting methods provide flexibility for extracting cross sections from the river topographical data.1
Cutting Cross Sections Automatically
The Automated Section Cut command can automate the extraction of river cross section geometry along a river centerline alignment at a pre-defined spacing. click River tab > Input panel > Create Section drop-down > Automated Section Cut.2-32
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
2. To automatically cut cross sections. specify the following parameters: River Centerline This entry is used to interactively select the river centerline alignment from the surface. Up to 800 cross sections can be extracted per river reach (this is a HEC-RAS limitation). and what to do when cross sections might overlap. cross section numbering. After selecting the river centerline alignment (at the downstream end). This allows you to adjust the cross section extraction polylines interactively. For example. In the Automated Section Cut dialog box. specifying additional parameters regarding cross section spacing.
2. The alignment should be selected from near the downstream end so that the software can determine the direction of the river in order to number the cross sections in increasing order while traversing upstream along the selected alignment. This cross section cutting method is the most commonly used method.7
Automated Data Extraction Methods
In addition to the manual methods for constructing cross sections. the software provides automated methods for extracting cross section geometry and other related data from the digital terrain map. The alignment should be a 2D or 3D polyline that is aligned perpendicular to how the cross sections are to be extracted from the surface. Template Cutline Enables you to provide a template cutline in order to have uniformity in the extracted cross section. grabbing the grips of the polylines to more precisely position where the cross sections are to
. the cross sections should be identical in geometry except for elevation.

Click Pick to interactively select the previously drawn cross section cutline(s). This option is disabled (not available) when using Template Cutline and Multiple Cutlines as the Cross Section Cutting Method. Cross Section Cutline(s) Selects the cross section cutlines when the Template Cutline and Multiple Cutline methods are selected as the Cross Section Cutting Method.
. Cross Section Spacing Specifies spacing to be used when extracting the cross sections along the specified river centerline alignment polyline. the software only extracts geometry data where terrain data exists (i. by either interpolating or extrapolating. contour lines). Therefore. Cross Section Width Specifies the width of the cross section to be extracted from the surface. this value ranges from 500 to 1500 ft—depending upon the study requirements.. This option causes the software to compute. the extracted cross section will generally be shorter than the specified cross section width or the selected cutline. This entry represents how wide the cross section will be.Using the Program
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be extracted. the corresponding elevation for the end points of the extracted cross section geometry. More detailed models require closer cross section spacing. where 1/2 of this width will be on each side of the previously drawn river centerline alignment. Click < to interactively select the cross section spacing distance. This option is disabled (not available) when using Multiple Cutlines as the Cross Section Cutting Method.e. Click < to interactively select the cross section width. Keep End Points of Cutline When extracting cross section data from a surface. Typically. This option is disabled (not available) when using Perpendicular as the Cross Section Cutting Method. This method will then automate the processing of these extraction polylines using the Section Cut by Object command (see section titled Cutting a Section from a Polyline on page 2-21).

The following reference station Types are provided: • • • • Centered Leftmost Station Rightmost Station Thawlag Centerline
Click Pick to interactively measure the distance to be used for the reference station numeric value. The following methods are provided: • • • • Parallel to Intersecting XS Trim Intersecting Ends Allow Overlapping XS Delete Overlapping XS
Figure 2.2-34
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
XS Overlapping Different cross section cutting methods provide flexibility for extracting cross sections from the river topographical data.1 Different methods to handle overlapping cross sections
Reference Stationing (optional) This option allows you to specify a reference station and corresponding numeric value for the geometry cross section data to be extracted from the surface.7.
.1.

meters. To assign bank stations and reach lengths.7. Click Pick to interactively select the downstream end of these alignment polylines.2
Assigning Bank Stations and Reach Lengths
The Assign Bank Stations and Reach Lengths commands can automate the extraction of this cross section data from alignments drawn on to the topographical map. click River tab > Input panel > Section Assign drop-down > Assign Bank Stations & Reach Lengths. In the Automated Bank Stations & Flow Lengths dialog box. meters. right overbank distance (in ft. corresponding to where the specified alignment polylines intersect the extracted cross sections. Alternatively. The channel flow length is already determined using the specified river centerline alignment polyline.Using the Program
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Bank Stations (optional) This option allows you to specify alignment polylines that represent the left and right bank stations. The following methods are provided: • Fixed • Channel Reach Length • Average Reach Length A fixed amount is used to increment the cross section ID The channel reach distance (in ft. Cross Section ID Increment Specifies how the cross section ID increments. Cross Section ID This section allows you to specify how the cross section IDs are to be assigned. Ground stations will be added to the extracted cross section geometry. Overbank Flow Lengths (optional) This option allows you to specify alignment polylines that represent the left and right overbank flow lengths. left overbank. specify the following parameters:
. or kilometers) is to be used to determine the cross section ID The average of the channel. miles. the left and right bank alignment polylines can be used for determining these flow lengths. Click Pick to interactively select the downstream end of these bank station alignment polylines. Starting Cross Section ID Specifies the ID of the downstream most cross section. or kilometers) is to be used to determine the cross section ID
-
2. miles.

straight lengths of river. Click Pick to interactively select the downstream end of the river centerline alignment polyline. corresponding to where the specified alignment polylines intersect the cross sections. Ground stations will be added (or burned in) to the existing cross section geometry. The following methods for computing these lengths are provided: Use Bank Lines This option is used when the previously specified alignment polylines that represent the left and right bank stations represent the overbank flow lengths. Use Overbank Flow Length Lines This option is used to specify alignment polylines that represent the left and right overbank flow lengths. the software will determine the distance between cross sections and then enter this as the channel flow length. Click Pick to interactively select the downstream end of these bank station alignment polylines. then this option causes the software to compute the channel flow length by subtracting the difference between the cross section IDs (from the current cross section and the next downstream cross section). Using this alignment polyline. Overbank Flow Length (optional) This option is used to automatically compute the overbank flow lengths for the selected cross sections (or current river reach). Channel Flow Length (optional) This option is used to automatically compute the channel flow length for the selected cross sections (or current river reach). Use Channel Flow Length This option is used when the overbank flow lengths are roughly equal to the defined channel flow length.2-36
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Bank Stations (optional) This option allows you to specify alignment polylines that represent the left and right bank stations.
. This option can be selected when defining long. Use Cross Section ID Difference If the cross sections have been numbered based upon their river stationing. Use River Centerline This option is used to interactively select a river centerline alignment from the surface. The alignment should be a 2D or 3D polyline that is aligned with the centroid of the channel flow area. Click Pick to interactively select the downstream end of these alignment polylines. The following methods for computing this length are provided.

The polygon’s elevations need to be set equal to the desired Manning’s roughness value for the software to assign the appropriate roughness.3
Assigning Manning’s Roughness
The Assign Manning’s Roughness command can automate the extraction of Manning’s roughness from the topographical map. defined on the specified layer with the previously defined cross sections.055 to be defined. the elevation of the polygon should be set to 0. The software will then intersect the polygons. click River tab > Input panel > Section Assign dropdown > Assign Manning’s Roughness. The following selections are provided: • All cross sections (current reach) • Selected cross sections
2. In the Assign Manning’s Roughness dialog box.7.7. polygon intersections occur. To assign Manning’s roughness.
. or can be used to assign default Manning’s roughness values. For example. specify the following parameters: Manning’s Roughness Polygon Mapping This optional section allows you to select the AutoCAD drawing layer that contains digitized polygons which represent corresponding Manning’s roughness values. thereby mapping the roughness values to the cross sections where these cross section vs. or the elevation value of the polyline.1 Example of overbank flow length mapping
Apply To This section is used to select to apply these specified automation data extractions to the current river reach or selected cross sections along the river reach.2. for a Manning’s roughness coefficient of 0.055.Using the Program
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Figure 2.

click River tab > Input panel > Section Assign dropdown > Assign Ineffective Flow Areas. The polygon’s elevations need to be set equal to the desired ineffective flow area elevation for the software to assign the appropriate areas. or selected cross sections.7.1 Example of Manning’s Roughness polygons
Default Roughness Values Defines the default Manning’s roughness for the left overbank.4
Assigning Ineffective Flow Areas
The Assign Ineffective Flow Areas command can automate the extraction of ineffective flow areas the surface. The following selections are provided: • All cross sections (all river reaches) • All cross sections (current river reach) • Selected cross sections
2. the current river reach. and right overbank areas at each cross section. These values are used where there are no polygon coverages defined.3. channel. To assign ineffective flow areas. In the Assign Ineffective Flow Areas dialog box.7.2-38
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Figure 2. The software will then
. specify the following parameters: Ineffective Flow Area Polygon Mapping This section allows you to select the AutoCAD drawing layer that contains digitized polygons which represent corresponding ineffective flow areas. Apply To This section is used to select to apply these specified automation data extractions to all river reaches.

The following selections are provided: • All cross sections (all river reaches) • All cross sections (current river reach) • Selected cross sections Permanent This check box denotes that the defined ineffective flow areas should be permanently defined in the model. click River tab > Input panel > Section Assign drop-down > Assign Levees. To assign levees. or selected cross sections.4. specify the following parameters: Left/Right Levee Line This section allows you to specify alignment polylines that represent the left and right levee stations. polygon intersections occur. thereby mapping the ineffective flow areas to the cross sections where these cross section vs. In the Assign Levees dialog box.7. the current river reach.
. Click Pick to interactively select the levee station alignment polylines.Using the Program
2-39
intersect the polygons defined on the specified layer with the previously defined cross sections. the ineffective flow areas can begin to carry conveyance once the ineffective flow area elevations have been overtopped by the computed water surface.
2.5
Assigning Levees
The Assign Levees command can automate the extraction of levees the surface.7.1 Example of ineffective flow area polygons
Apply To This section is used to select to apply these specified automation data extractions to all river reaches. Otherwise.
Figure 2.

The following methods for specifying the levee elevation are provided: Ground Elevation at Levee Station Location This option causes the software to use the existing ground elevation at the levee location.7.
2.
.7. described on page 2-38. Maximum Ground Elevation Along Overbank This option causes the software to use the maximum ground elevation defined for the overbank area geometry.2-40
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Figure 2. To assign conveyance obstructions. Fixed Elevation This option allows you to specify the elevation for the left and right levees.1 Example of levee mapping
Levee Elevations This section is used to assign the levee elevation. Maximum Ground Elevation at Cross Section This option causes the software to use the maximum ground elevation defined for the cross section geometry.6
Assigning Conveyance Obstructions
The Assign Conveyance Obstructions command can automate the extraction of conveyance obstructions from the topographical map. click River tab > Input panel > Section Assign drop-down > Assign Conveyance Obstructions.5. The Assign Conveyance Obstructions dialog box data requirements are nearly identical to the Assign Ineffective Flow Areas dialog box.

1
Entering Data Interactively
The software has been designed to make developing a water surface profile model easy and flexible by providing a variety of interactive input methods. and associated dialog boxes are covered in Chapter 3.8. For example.
.
2.Using the Program
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2.
2. Most data used to describe a HEC-RAS model is defined using interactive dialog boxes. you can develop a model by first importing an existing HEC-RAS or HEC-2 data file and then modifying the data. including importation of partial HEC-RAS or HEC-2 data files and XYZ coordinate data files. When grips are enabled. However. allowing complete flexibility while defining the ground geometry.8. you may need to use and modify a pre-existing HEC-RAS model which was developed without the software. which uses only one file for defining an analysis model. As you define modeling cross sections and associated data. a pickbox appears at the center of the cross-hair cursor. Many times. HEC-RAS data input requirements.PRJ) has to be selected for importing.3
Importing Existing HEC-RAS Files
The software stores its HEC-RAS information in the drawing file as extended entity data. using grips you can perform ground geometry adjustments graphically by simply selecting ground points and dragging them to their new location. HEC-RAS uses several files for defining a model. only the HEC-RAS project file (*. Or. methods.8. For example. You can enter data into the model using a variety of input methods. the software stores this information directly in the drawing file. These dialog boxes allow you to quickly comprehend what data input requirements are needed to define the model. The software will use the project file to determine the name of all the other associated HEC-RAS files. allowing you to immediately select and edit an object. And any of these methods can be used with any other. An external file is not used to store this information.2
Graphical Editing using Grips
AutoCAD allows you to edit selected objects by manipulating grips that are displayed at the defining points of objects. Similarly. over seven distinct methods exist for defining a cross section's ground geometry.8
Entering Data
Autodesk River Analysis is extremely flexible in how a water surface profile model can be developed.
2. Grips are configured in the AutoCAD Options dialog box. The software can directly import these models. however. ineffective flow area adjustments can be performed by simply selecting the polyline that describes the ineffective flow area and adjusting it. Unlike HEC-2.

the software will display the Add Reach dialog box. In the Import HEC-RAS Project dialog box. the software allows you to link the imported cross sections and related information to a topographical map. The HEC-2 analysis engine uses this file to perform the water surface profile analysis. which allows you to specify the new river reach ID for this data to be imported into. the software stores this information directly in the drawing file. When you generate a HEC-2 input data file (see the section titled Model Checking on page 2-47). navigate to the HEC-RAS project file.
.
2. As you define cross sections and associated data.
Linking to a Topographical Map
If the original HEC-RAS model was digitized in real world coordinates. Click River tab > Create Reach Data panel > Import drop-down > Import HECRAS. An external file is not used to store this information. the software writes out a HEC-2 data file (also called a card file). the Import Options are not available.2-42
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
To import a HEC-RAS model: 1.8.
3. As the software imports the project. the software replaces the existing cross section ground geometry with new geometry.
2. However.
•
After you select a HEC-RAS project file. For example. Specify whether to import the data into the current river model or a new river model: • If you request that the data be imported into the current river reach.4
Importing an Existing HEC-2 Data File
The software stores its HEC-2 information in the drawing file as extended entity data. if an identical cross section ID is encountered in the external data file as is specified in the current river reach. If you request that the data be imported into a new river reach. See the section titled Tracing a Cross Section Cut Line on a Surface on page 2-29. 4. if the original model was not developed using real world coordinates. the software allows the imported data to overwrite any matching data which might already be specified in the river reach. the software imports the project's HEC-RAS modeling data into the drawing. it will report its status at the AutoCAD command line. specify whether to use an imported HEC-RAS river alignment. In the Import HEC-RAS Project File dialog box. This file describes the defined HEC-2 model. then the imported model will already overlay on the corresponding topographical map. Data import errors and warnings will be displayed. allowing you to later correct the imported data. If the drawing does not contain any existing HEC-RAS data.

3.
2. the software will report this as an error. This import method allows cross sections to be added to the current river reach. or added to a new river reach. the software replaces the existing cross section ground geometry with new geometry. The software can directly import these files. To import a HEC-2 data file: 1. navigate to the HEC-2 project file.
Cross Section Numbering
When importing a subcritical HEC-2 data file. If you request that the data be imported into the current river reach. In the Import HEC-2 dialog box. This allows you to import multiple cross sections using a single survey file. specify whether to import the external data into the current river reach. To import preexisting HEC-RAS data files.
Linking to a Surface
The software allows you to link the imported cross sections and related information to a surface. the cross section identification numbers must be defined in the data file in ascending sequential order. as shown in the following figure. If a cross section identification number is found to be out of order. enter RMS_ImportXYZ at the command line.8. To import survey cross section data. if an identical cross section ID is encountered in the external data file as is specified in the current river reach. the software will display the Add Reach dialog box. cross section identification numbers must be defined in descending sequential order. See the section titled Tracing a Cross Section Cut Line on a Surface on page 2-29.5
Importing Survey Cross Section Data
The software can import XYZ or YXZ (Northing-Easting) coordinate data for multiple cross sections. or cancel the import request. in the Import HEC-2 Data File dialog box. the software allows the imported data to overwrite any matching data which might already be specified in the river reach. Click River tab > Create Reach Data panel > Import drop-down > Import HEC2. please refer to the previous section beginning on page 2-41. The software will display the Import Coordinate File dialog box if cross section data is
. Similarly. If there is existing HEC-2 data in the drawing. when importing a supercritical HEC-2 data file.Using the Program
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You may need to use and modify a pre-existing HEC-2 data file that was developed without using the software. assign a new river reach to the data being imported. If you request that the data be imported into a new river reach.
2. For example. if a surface exists. This dialog box allows you to specify the new river reach ID for this data to be imported into.

For example. The following options are available for importing cross sections using coordinate data. the software displays a file selection dialog box for importing the cross section coordinate data file. This option is especially useful when linking a previously imported HEC-2 model to the topographical map. this check box is selected. then this option will only update the cross section locations on the topographical map. If there are no cross sections defined for the current river reach. If this check box is cleared. By default. Import into Current River Reach Imports cross sections into the current river reach. In this situation. rather than displaying the Import Coordinate File dialog box. the file must be formatted properly. thereby linking these existing cross sections to the topographical map. the cross section geometry from the original HEC-2 model is maintained. After specifying how the data is to be imported. allowing you to define how the data file is to be imported. where you specify whether to create topographical map links. if cross sections already exist in the model and their specified ground geometry is adequate. then only the station-elevation cross section data is imported into the drawing file. When this option is selected. Create a New River Reach Imports the cross sections into new river reach. the software prompts you for a new river reach ID for the cross sections to be imported into. the software displays the Create Topographical Map Links dialog box. but the cross sections are then linked to the topographical map. If any of the imported cross sections have a cross section ID that is duplicated in the current river reach. Create/Update Topographical Map Links Only Imports only the XY (or YX) topographical map coordinates for pre-existing cross sections.
.2-44
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
already contained within the current river reach. Cross sections contained in this file that have no equivalent in the drawing file will be ignored. The cross section stationing and elevation data will remain the same. at the XY (or YX) topographical map coordinates specified in the imported file. This allows you to create a 2D cut line file that the software is to use in cutting cross sections from the topographical map. this imported cross section data replaces the existing cross section data for the duplicated cross sections. Create/Update Topographical Map Links Causes the cross sections to be drawn on the topographical map. as described in the section titled Recutting a Cross Section on page 2-30. This option can be used in with recutting the cross section ground geometry from the topographical map.
Multiple Cross Section Data File Format
For the software to be able to identify that the file being imported is a multiple cross section XYZ or YXZ (Northing-Easting) coordinate data file.

The second and third lines in the file denote the unit base of the data contained in the file. The sixth line defines the ID of the first cross section contained in the file. and Z coordinates) of a single 3D ground point for the cross section. The first line in the multiple cross section data file must contain the keyword XYZ (or YXZ) by itself. These lines can have the keyword Imperial or Metric. The third line denotes the elevation (Z) coordinate unit base. The fifth line in the file is used to define an elevation datum adjustment value for all of the cross sections being imported. The starting horizontal station value cannot be negative. Each ground point's Z coordinate value is added to the specified elevation datum adjustment value to determine the resulting elevation. then the imported data is converted to the drawing file unit base. commas.0 is assumed.
5.
. being added to the specified starting horizontal station value to determine each ground point's resultant stationing value. However. The following figure illustrates that the surveyed ground points do not need to reside along a straight line. If this line is left blank. X.
3. The cross section ID number should not be longer than 6 characters. To mark the start of another cross section. and then the cross section ID number.0 is assumed. including the decimal point if one is defined. these surveyed points should form a line perpendicular to the stream flow. and/or tabs can be used to delimit the coordinate values of each point.
4.
2. 7. The remaining lines in the file correspond to the X. and Z coordinates (or Y. Spaces. This line should start with XS. followed by a space. If this line is left blank. This adjustment value allows you to adjust the elevation of the coordinate data. This distance is accumulated. a blank line must be inserted which is then followed by a cross section ID line (as described previously).
6. an elevation adjustment of 0. Negative or positive coordinate values are allowed.
The software uses the Pythagorean Theorem to determine the absolute distance between adjacent ground point stations using the specified X and Y coordinate values. If the unit base for either the XY or Z data is different than that of the drawing file unit base (see the section titled Configure Elevation Precision on page 2-88). a starting horizontal station of 0. The second line in the file denotes the XY coordinate unit base.Using the Program
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Follow these guidelines when developing a coordinate data file: 1. Y. The fourth line in the file defines the starting horizontal station value for all of the cross sections being imported.

Additional error checking is performed during the analysis. but should form a line perpendicular to the stream flow
2. enabling you to correct the faulty data. as opposed to errors. To specify the analysis options.2-46
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Figure 2.8. click River tab > Analysis panel > Analysis Options.9.
.1 Surveyed ground points do not need to lie along a straight line.1
Defining Analysis Options
The Analysis Options dialog box provides a number of options to control how the analysis is to be performed.8.6
Data Entry Checking
Data entry checking is performed by a model checker that is integrated into the software. the software describes the error in a dialog box.9
Model Analysis
Once you have defined a HEC-RAS water surface profile model.
2. If an error is detected during data entry within a dialog box. Data checking is performed both during actual data input and during preparation of the intermediary input data file used during the analysis. The model checker allows you to use the value. Many common data entry errors are discovered immediately. which must be corrected before you click OK. the message displayed is only a warning or suggestion.
2.5. Note that for some dialog box entries. The following sections describe how to perform an analysis. you are ready to perform an analysis.

9. geometry. To export the current river model to a HEC-RAS project data file.
2. Click River tab > Create Reach Data panel > Export HEC-RAS Project. it displays an Alert dialog box that describes the omission and identifies which command should be issued to insert the missing input data. specify a name and location for the HEC-RAS project file. 2. and plan files) using the standard US Army Corp file format.9. and P01 (plan file). if the software determines that some input data is missing.9. click River tab > Analysis panel > Compute Analysis. The software checks the model for data entry errors. it reports its status at the command line. F01 (flow file). and then executes the HEC-RAS analysis engine.Using the Program
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2. profile
.
The software exports the standard HEC-RAS project data files with the filename extensions of PRJ (project file).
Errors and Warnings
If an error is reported during the creation of the intermediary input data file. builds the intermediary input data file for the HEC-RAS analysis engine to run. allowing you to correct the input data. In the Export HEC-RAS Project dialog box. If a warning is reported. as well as displaying the graphical results on the cross section grids.3
Model Checking
When the software generates the intermediary input data file from the defined input model.2
Performing a HEC-RAS Analysis
After the HEC-RAS model has been defined. The software can display a summary of the analysis results. the software displays a message detailing the error.10 Displaying Analysis Results
After running the water surface profile analysis for the current river reach. the analysis can be performed. Modeling errors and warnings are displayed. flow. the software can display the analysis results. project.e. G01 (geometry file).
Missing Input Data
While generating the intermediary input data file.
2. If a problem is detected in the defined model data. you must correct the model before the analysis can be performed.4
Exporting a HEC-RAS Project
The software can import and export HEC-RAS project data files (i.
2. 1.. The software reports a warning when it has determined that there may be difficulty in performing a water surface profile analysis with the defined model.

profile table view.10. In the River Scenario Analyzer. To plot the rating curve: 1. Plots menu in the River Scenario Analyzer.2-48
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
grids. click on the General Profile Plot icon the Scenario Analyzer toolbar.
2.
. To display the general profile plot: 1.1. click River tab > Output panel > Results Viewer drop-down > Profile Summary Plot.10..10. from
2. The YAxis Variables dialog box is displayed. allowing you to view numerous variables along the river profile.1. and surface.10. In the River Scenario Analyzer.
2.
2.2 General Profile Plot
The River Scenario Analyzer can plot a generalized profile plot. Any input or output variable can be selected for plotting.1
River Scenario Analyzer
Autodesk River Analysis provides a powerful River Scenario Analyzer that allows you to view HEC-RAS output results. In addition. These results can be viewed in a cross section table view.
2. click on the Rating Curve Plot icon .. results from different models can be compared.] button adjacent to the Y Variable(s) entry. Click River tab > Output panel > Results Viewer drop-down > Profile Summary Plot.
You can change the displayed variables using the Std. You can customize what is displayed using the property sheet immediately to the left of the profile plot. and a profile plot view. allowing you to select the appropriate variables to plot.
2. Click River tab > Output panel > Results Viewer drop-down > Profile Summary Plot. The following sections describe in detail how to display these results. From the property sheet. click the browse [.3 Rating Curve Plot
The Scenario Analyzer can plot a rating curve. which displays the water surface elevation profile plot. The software opens the River Scenario Analyzer.1 Profile Summary Plot
To display a profile summary plot.1. allowing you to view numerous variables at a cross section.

click River tab > Output panel > Results Viewer > Cross Section Tables. select User Tables > Save Table. allowing you to define the table name and corresponding table description for later reuse. The software starts up the River Scenario Analyzer and displays the water surface profile results table.
Saving and Managing Custom Tables
Once a custom profile table has been created. The Tables menu in the River Scenario Analyzer lists the available cross section tables. select User Tables > Manage Tables. The software starts up the River Scenario Analyzer and displays the cross section results table for the current cross section. it is removed from the User Tables menu. The Save Table dialog box is displayed.
2.4 Profile Tables
To display a profile table.Using the Program
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You can change the variables displayed on the rating curve. From the River Scenario Analyzer.5 Custom Profile Tables
You can generate custom profile tables containing any input or output variable. If a custom profile table is deleted. it is listed at the bottom of the User Tables menu. allowing you to select the appropriate variables to plot. Note that cross section tables that are not available are grayed out in the menu. Several different pre-defined profile tables are available.. In the River Scenario Analyzer.] button adjacent to Y Variable(s) entry..1. The Y-Axis Variables dialog box is displayed. Decimal precision and other options are available. click River tab > Output panel > Results Viewer > Profile Tables. allowing you to make necessary table name change or to delete a table. The Define Table dialog box is displayed. select User Tables > Define Table.
2. The Manage Tables dialog box is displayed. From the property sheet.10. Tables menu in the River Scenario Analyzer lists the available profile tables.1. click the browse [. To rename or remove a previously defined custom profile table. The Std.6 Cross Section Tables
To display a cross section table. allowing you to select the variables to be included in the current table.10.
2.1.
. its definition can be saved for later reuse. Once the custom profile table has been defined. on a variable by variable basis. Several different pre-defined cross section tables are available.10.

10.2
Displaying Cross Section Results
The software can quickly plot the analysis results on the cross section views in the AutoCAD Civil 3D drawing..10. profile table.
2. The Cross Section Results dialog box allows you to specify exactly which results will be displayed on the cross section views. Alternatively. Then. click River tab > Output panel > Section Results drop-down > Add Section Results. To display the graphical results on the current river reach cross section grids.1. on the left navigation panel. to reload the new analysis results into the River Scenario Analyzer.e. To copy the results to the clipboard for pasting into another Windows application (e. you can click on the view to be displayed.g. select File > Print. either select File > Reload Data or press Ctrl+R. Microsoft Word.
.9 Switching Units
To switch units bases.).
2.. Microsoft Excel. select either Edit > Copy Selected Cell(s) or Edit > Copy Table. you must select more than one profile in the profile list box.
2.1. The River Scenario Analyzer can display results in both English and metric (SI) units. If more than one profile's results are to be displayed.1.10.
2.10. the following results will be displayed on the cross section grids for the current river reach: • • • • • Flow discharge Known water surface Computed water surface Critical water surface Energy grade line
The results are added to the cross sections views on a profile-by-profile basis. If the appropriate check boxes are selected.7 Switching Summary Views
The River Scenario Analyzer allows you to switch between various summary views (i. Various options are provided to meet various reporting requirements. etc. and cross section table).10. use the Options menu.1. profile summary plot.10Reloading the Analysis Results
The River Scenario Analyzer can continue to run while you make modifications to the model and re-run the analysis.8 Outputting Summary Results
To output the results displayed in the Scenario Analyzer to a printer.2-50
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
2. Use the View menu to switch between the summary views.

Profile views must exist before any graphical results can be displayed.
2. However. special bridge/culvert/roadway symbols.3
Displaying Profile Results
The software can quickly generate profile plots along the river. The accumulated channel reach lengths are used as river stationing values for the profile view horizontal axis. and known water surface elevation. you can define profile views for the software to use in displaying the water surface profile results. For information on how to create profile views.10. However.3. The profile grid displays the natural channel invert. a single profile view can be used to display the entire water surface profile. Various options are provided. and legend text for the results. energy grade line. The cross section river stationing is determined by adding together the channel reach lengths defined for each cross section. click River tab > Output panel > Profile Views > Add Profile Results. linetype. critical water surface. Profile views can be added to the drawing either before or after the analysis has been performed.
2. The profile view horizontal axis denotes the river stationing (in feet or meters) of the defined cross sections.10. for larger models.3.
Removing the Cross Section Results
Click Erase to remove all plotted graphical results from the cross section views. each of these cross section graphical results has a corresponding Options button. computed water surface.1 Profile Views
Once the cross section geometry has been defined for a model. Profile views can be added to the drawing either before or after the analysis has been performed. multiple profile grids may be specified to display the water surface profile results in manageably sized portions.10. For small models. see the section titled Creating a Single Profile View. allowing you to specify the color. where the reach of river being studied is longer than the typical length of a profile view. left and right overbanks. to meet various reporting requirements. water surface profile results can only be displayed on the defined profile grids if a water surface profile analysis has been performed. See the section titled Displaying Profile Results on page 2-51 for information on how to specify how the analysis results are to be displayed on the profile grids.2 Displaying Profile Results
To display the graphical results on the current river reach profile views. These options apply only to the currently highlighted profile in the list box.
. The Add Profile Results dialog box provides numerous options for plotting the profile results. Different display options can be set for each profile.
2.Using the Program
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In addition.

enough profile views will be created to display data for the entire river reach length. and cannot be left blank. each of these profile view graphical results has an Options button.3. Different display options can be set for each profile. which is determined by adding the reach lengths of all cross sections. This value defaults to the number following the last existing profile view’s ID. legend text. If the appropriate check boxes are selected.
. Grid generation will stop when this channel reach length is attained. For each selected profile. and data point symbol for the results. if any profile view with the same ID already exists in the current river reach. In the Create Profile Views dialog box. Starting Grid ID Specifies the unique ID of the first profile view to be generated. specify the following parameters: Number of Grids (optional) Specifies how many profile views will be generated.2-52
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
The Add Profile Results dialog box allows you to specify which results to display on the profile views.3 Creating Multiple Profile Views
To create multiple profile views for the current river reach. by checking the profiles of interest in the selection list. even if a larger number of views has been specified in this entry.
2. Starting Station Defines the starting river station (in feet or meters) of the first profile view’s horizontal axis.10. Note that these options apply only to the currently highlighted profile in the list box. the following results will be displayed on the profile views for the current river reach: • • • Computed water surface Critical water surface Energy grade line
You can select profile results to plot. you can control which results to be plotted. This entry must be positive. For each new grid. click River tab > Output panel > Profile Views > Create Profile Views. on a profile-by-profile basis. the increment will be added again until a unique ID is found. If left blank. In addition. linetype.
Removing the Profile Results
Click Erase to remove all plotted graphical results from the profile views. allowing you to specify the color. Grid ID Increment Specifies the increment to be added to the starting grid ID to determine the IDs of the second and subsequent profile views generated.

If the appropriate check boxes are selected. but you may start the profile reach at any station. Starting Elevation (optional) Defines the starting (lowest) elevation (in feet or meters) for each generated profile view’s vertical axis. smaller. and a shorter length will produce more. This entry can be positive or negative.
. must be displayed using the Profile Results dialog box after the water surface profile analysis is run. and roadway elevations Cross section IDs
Each profile grid cross section data item has a corresponding Options button. all non-computed data is displayed. Profile Geometry Data This section allows you to select which profile data will be displayed on the profile views. profile views. If this entry is left blank. each view's starting station will equal the previous view’s ending station.0. the software determines this height for each profile view by finding the height of all data to be displayed on the profile view. legend text. If this entry is left blank. This height will be added to the starting elevation to determine the ending (highest) elevation of the profile view vertical axis. This length will be added to the starting (downstream) station to determine the ending (upstream) station of each profile view’s horizontal axis. If the Number of Grids entry is left blank. This value defaults to 0. the software determines this elevation for each profile view by finding the minimum elevation of all data to be displayed on the profile view. By default. profile views. Axis Height (optional) Defines the height (in feet or meters) of each profile view's vertical elevation axis. See the section titled Displaying Profile Results on page 2-51 for more information. This entry may not be changed after a profile view has been added to the current river reach. This entry must be positive. and data point symbol to be used. a longer axis length will generate fewer. linetype. low chord. Downstream XS Station (optional) Defines the river station at which the most downstream cross section is located.Using the Program
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Axis Length Defines the length (in feet or meters) of each profile view’s horizontal stationing axis. but larger. allowing you to specify the color. the following data will be displayed on the profile view(s) being added or edited: • • • • Natural channel invert Left and right overbanks Bridge and culvert invert. Computed results. For the second and subsequent profile views. such as the hydraulic grade line. This entry must be positive in value.

you might want to display this modified data on existing profile views.6 Refreshing Profile View Data
After modifying geometry data to cross sections. roadway geometry.
2. and water surface profile elevations).7 Panning and Zooming to a Profile View
The Zoom to Profile View dialog box allows you to select and view a profile view.
2. click River tab > Navigate panel > Zoom to Profile View.) To refresh profile view. The Edit Profile View entries are identical to those described in the section titled Creating a Single Profile View on page 2-54.5 Editing a Profile View
The Edit Profile View dialog box allows you to edit an existing profile view’s attributes.
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Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
2. The Edit Profile View dialog box is often used to manually edit an existing profile view to turn on and off profile related data (such as ground geometry.3. Select a profile view from the Zoom to Profile View dialog box to display a profile view.10. enter RMS_ProfEdit on the command line.3.8 Resizing Profile Views
The software can automatically resize the grid to the extents of the profile view’s data.10. enter either RMS_ProfPrev or RMS_ProfNext on the command line.
.3. To zoom to a profile view.3. (Profile views are not automatically updated.10. click River tab > Output panel > Profile Views > Delete Profile Views.
Navigating Among Profile Views
To zoom to previous or next profile views. click River tab > Output panel > Profile Views > Update Profile View Data. such as adding a bridge or culvert structure.10.
2. To edit a profile view.
Manual Erasing
The AutoCAD Erase command can be used to delete any of the AutoCAD River Analysis entity data.4 Deleting Profile Views
To delete one or more profile views.3.10.

. Intersected Edge of Water Causes an interpolated edge of water to be drawn on the surface. The following results may be generated for the currently selected profile. you must select more than one profile in the profile list box. the edge of water is not interpolated between cross sections) using the reported left and right edge of water from the simulation results. The edge of water will be drawn using straight line segments between cross sections (i.e. Various options are provided. The Configure Profile Views dialog box (see the section titled Configure Profile Views on page 2-84) provides configuration settings controlling how grid axes are to be resized. Click Options to display the Straight Line Edge of Water Options dialog box. which allows you to display the water surface profile on the surface on a profile-by-profile basis. click River tab > Output panel > Profile Views > Resize Profile Views. Click Options to display the Intersected Edge of Water Options dialog box. and then intersecting these two surfaces with each other to determine a precise edge of water. See the section titled Intersected Edge of Water Option on page 2-58 for more information on this floodplain mapping option. so selecting them for one profile does not select it in any other profile.Using the Program
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To resize profile views. which presents various options for drawing the straight line edge of water. nothing will be plotted on the surface.4. If more than one water surface profile is to be displayed. Selecting another profile in the list box displays the current settings for that profile only. Straight Line Edge of Water Causes a straight line edge of water to be drawn on the surface between cross sections.10.1 Floodplain Mapping Options
To create a floodplain map on the topographical map. The software will interpolate the edge of water between cross sections by building a digital terrain model (DTM) of the ground topography and of the computed water surface elevation.
2. These results have individual settings for each profile. This displays the Floodplain Map Results dialog box. See the section titled Straight Line Edge of Water Option on page 2-59 for more information on this floodplain mapping option. If no profiles were selected when you click OK. click River tab > Output panel > Flood Map drop-down > Add Floodplain Map. which presents various options for drawing the intersected edge of water.
2.4
Displaying Floodplain Map Results
The software can quickly generate detailed floodplain maps from the computed model results. to meet various floodplain mapping requirements.10..

representing the depth of the flood.3 shows two uncertainty lines—corresponding to ± 0. Depth Specifies the depth. Flood Elevation Contours (BFE) This option is used when plotting the intersected edge of water floodplain map. in feet or meters. a value of 1 shows all areas of the water surface where the depth is less than or equal to 1 foot (or meter). For example. For example. which presents various options for drawing the depth contours as well as to specify the depth contour interval. a value of 1 generates 1 foot (or meter) contours. a value of 1 generates 1 foot (or meter) contours. Flood Uncertainty Band This option is used when plotting the intersected edge of water floodplain map. Flood Depth Contours This option is used when plotting the intersected edge of water floodplain map. for which shallow flooding is displayed. and causes the software to draw base flood elevation (BFE) contours. Contour Interval Specifies the interval at which contours of elevation are generated. Click Options to display the Flood Depth Contours Options dialog box. For example. which presents various options for drawing the shallow flooded areas as well as what the shallow depth value should be. Click Options to display the Shallow Flooded Areas Options dialog box. which presents various options for drawing the uncertainty band as well as to specify the uncertainty in the ground terrain elevation data.2-56
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Shallow Flooded Areas This option is used when plotting the intersected edge of water floodplain map.
. A negative depth value shows all areas outside the water surface that would be flooded should the current computed water surface rise by that amount. and causes the software to draw where the flood depth is less than that of the specified shallow depth value. Click Options to display the Flood Elevation Contours Options dialog box. Terrain Error Specifies the amount of error to be plotted on the floodplain map in either elevation or percent error.3 ft (or m). and causes the software to draw on the topographical map the flood depth contours. For example. specifying an elevation value of 0. Click Options to display the Flood Uncertainty Band Options dialog box. which presents various options for drawing the BFE contours as well as to specify the BFE contour interval. Depth Interval Specifies the interval at which contours of flow depth are generated. and causes the software to draw the amount of uncertainty in the flood results based upon the amount of uncertainty in the ground terrain elevation data.

However. This option is used to limit the extent of the drawing to be considered when performing the terrain surface intersection with the computed water surface results—thereby speeding up the floodplain mapping process. this check box is cleared. Y coordinate entries. See the section titled Floodplain Mapping Problems on page 2-60 for more information on this option. the software will not be able to generate the interpolated edge of water results. if the ground terrain does change—such as when enabling a different set of drawing layers that represent post development ground terrain—then this check box should be selected. since the ground surface rarely changes. Therefore. For additional information. the software will use the text height specified in the Configure Topographical Map dialog box (see the section titled Configure Topographical Map on page 2-87). enter a value in the Text Height field. To specify a text height for the legend. The legend position on the topographical map is specified by the X. Click Pick to pick the legend position directly from the surface. By default. Even if this option is selected. and causes the software to make certain that any flooded areas contained outside of the main channel area are hydraulically connected. If this entry is left blank.Using the Program
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Topographical Map Ground Surface This data is used when plotting the intersected edge of water floodplain map.
. The legend identifies the floodplain map results plotted on the topographical map. see the section titled Configure Elevation Sources on page 2-84. depressions (or ponded areas) outside of the river’s flooded area will not be filled-in by the software when the floodplain is plotted—unless the outer flooded area is somehow connected with the river’s flooded area. Clipping Polygon This option is used when plotting the intersected edge of water floodplain map. Regenerate Ground Surface This option is used when plotting the intersected edge of water floodplain map. individual legends may be turned off by clearing the legend option within each Options dialog box. which allows you to specify the AutoCAD layers and/or Civil 3D surfaces that contain elevation data. Click Configure Layers to display the Configure Elevation Layers dialog box. and allows you to select the type of clipping polygon to use. Erase Previous Results Causes any previously plotted results to be deleted from the surface when plotting the new floodplain map results. Legend Specifies if a legend will be displayed on the surface. Restrict Mapping to Model Results This option is used when plotting the intersected edge of water floodplain map. If ground geometry information has not been defined. in order to speed up generation of the ground surface DTM. and causes the software to regenerate the ground surface DTM (Digital Terrain Model) when the floodplain map is plotted.

Click Define to display the Define GIS Coverages dialog box. and then intersecting these two surfaces with each other to determine a precise edge of water. By examining the constructed ground terrain 3D grid.
2.0 since it takes longer to compute an intersecting 3D polyline.10.
.4. The intersected edge of water may be drawn in one of several ways using the settings in the Intersected Edge of Water Options dialog box. Generate 3D Results This option is used when plotting the intersected edge of water floodplain map. Generate GIS Coverages Causes the software to generate shapefiles of the floodplain map results. and causes the software to construct a 3D grid of the ground terrain from the specified elevation data. you can then determine what elevation data is causing problems. This allows the topographical map view to be rotated and the edge of water boundary polyline will shown to intersect with the terrain.2 Intersected Edge of Water Option
The Intersected Edge of Water option on the Floodplain Map Results dialog box causes an interpolated line representing the edge of water to be drawn on the surface. The following options are available for drawing the intersected edge of water on the surface. This is useful in troubleshooting a floodplain map that does not appear correct. To display the dialog box. Fill Type An interpolated edge of water is generated by one of the following methods: None An interpolated edge of water is displayed using an unfilled boundary polyline. as well as of the defined input data. this option is disabled and a 2D polyline will be generated at an elevation of 0. The software interpolates the edge of water between cross sections by building a digital terrain model (DTM) of the ground topography and of the computed water surface elevation. click the Options button adjacent to the Intersected Edge of Water option on the Floodplain Map Results dialog box. These shapefiles are stored in a subdirectory that is created in the directory that contains the drawing file. and causes the software to construct 3D polylines for the edge of water polyline that follows the terrain surface where it intersects. This is the fastest method for generating the intersected edge of water. Note that by default. with the same name as the drawing file. which allows you to define specifically what input and output data should be written to GIS coverage shapefiles.2-58
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Generate 3D Grid of Ground Surface This option is used when plotting the intersected edge of water floodplain map.

a step size of 10 or 20 drawing units will provide sufficient detail without compromising computing time or storage space.
. to calculate the edge of water every foot (or meter). However.. allowing selection of a hatch pattern. Line Options This section allows you to specify color. in drawing units. Hatch The interpolated edge of water boundary polyline is filled with a hatch pattern.3 Straight Line Edge of Water Option
The Straight Line Edge of Water option from the Floodplain Map Results dialog box causes a straight line representing the edge of water to be drawn on the surface. press Esc to halt the hatch generation. The edge of water may be drawn in one of several ways using the settings provided in the Straight Line Edge of Water Options dialog box.e.10. set this entry to 1. the edge of water is not interpolated between cross sections) using the reported left and right edge of water from the simulation results. click the Options button adjacent to the Straight Line Edge of Water option from on the Floodplain Map Results dialog box. generating the hatch may take excessive amounts of time and drawing space. To display this dialog box. On most surfaces. If this turns out to be the case. and rotation angle. This fill is temporary. this area may be filled at any later time by entering RMS_FPMTopoFill on the command line. and linetype options for the simple water surface. scale. These options apply only to the current profile. The edge of water will be drawn using straight line segments between cross sections (i. which is not erased when the viewport is redrawn.Using the Program
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Temporary File The interpolated edge of water boundary polyline is filled with the polyline color. Hatch Options Displays the AutoCAD Hatch and Gradient dialog box. which can take excessive amounts of time and drawing space. Global Width Specifies line thickness for the drawn edge of water polyline. For example. legend. at which all water surface intersection results will be generated. Intersection Step Size Specifies the detail. Small step sizes (1 or less) will generate very complex contours. and will be erased the next time the viewport is redrawn.4.
2. Depending on the hatch options selected.

or is greater than the distance from one cross section to the next.
.4. Any ground terrain data outside of this bounding polygon is ignored and not included in developing the DTM. Note that these options apply only to the current profile. Segment Size Specifies the surface distance between segments of the 3D polyface mesh generated using the 3D or shaded mesh options above. This option is only available for the 2D Polyline edge of water option. The smaller the size. the software would extract all of the data from the specified elevation layers—thereby taking a great deal of time while it developed the DTM. Shaded Mesh The 3D mesh is shaded using the AutoCAD SHADE command. Global Width Specifies line thickness for the drawn edge of water polyline. The specified segment size and color are used. 2D Polyline A 2D polyline is drawn around the profile's water surface edges between each cross section in the specified color and linetype. and linetype options for the simple water surface. This is done to limit the amount of time required to develop a DTM for the area being modeled.
2. Type This list defines the type of straight line edge of water to be plotted. To limit the area to be used to extract ground terrain data.2-60
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
The following options are available for drawing the straight line edge of water on the surface. Otherwise.10. only one mesh segment will be generated between each cross section. the software creates a bounding (or clipping) polygon corresponding to the defined river cross sections. the more detailed the mesh (and the longer it takes to generate). 3D Mesh A 3D polyface mesh is drawn using the specified segment size and color. the software will limit the area that will be used to extract ground terrain data from the specified elevation layers when it builds its digital terrain model (DTM). Line Options This section allows you to specify color. legend.4 Floodplain Mapping Problems
When the intersected edge of water option is used to create the water floodplain map. 3D Polyline A 3D polyline is drawn around the profile's water surface edges between each cross section in the specified color. If this entry is left blank.

Inserting additional user-interpreted TIN data points can quickly correct this problem. Note that this may cause problems when generating the interpolated edge of water at sharp bends in the river where the bounding polygon does not extend out far enough to include the area where the water surface intersects the terrain model. this is generally due to a false dam being created when the digital terrain model (DTM) is created from the provided ground terrain data. and then capping these two polylines with each other using a straight line. additional cross sections may need to be inserted and/or the existing cross sections extended.Using the Program
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Figure 2. Generally this occurs with a sparse TIN point data set. where there is not enough data points within the channel to accurately depict the channel geometry. Any ground terrain data outside of this boundary polygon is ignored and not included in developing the DTM. Flooded areas that extend beyond this bounding polygon will be cut off. In these situations. Otherwise. the rightmost edge of all cross sections with a polyline.
False Dams and Insufficient Terrain Data Problems
If the floodplain mapping skips parts of the river channel (see the following figure) or is disjointed (breaks in the flooding). and will appear truncated with a stair-step edge.10.
.4.1 Example of the bounding polygon
The boundary polygon is constructed by connecting the leftmost edge of all cross sections with a polyline.4. This is done to limit the amount of time required to develop a DTM for the area being modeled. the software would extract all of the data from the specified elevation layers—thereby taking a great deal of time while it developed the DTM. This stair-step edge will correspond the specified step size.

2 A “false dam” can cause the floodplain map to skip parts of the river channel
A false dam occurs during the floodplain delineation tinning process when a TIN edge (one side of the TIN triangle) straddles the natural channel.4. A TIN is constructed by triangulating the vertices that define the ground terrain.4. existing TIN vertices.4.
Figure 2.10.10. etc. points.3 Two adjacent TIN triangles which (a) violate and (b) satisfies the Delauney criterion
. forming a dam across the channel. polylines. The software connects the vertices with a series of edges to form a network of triangles to represent the terrain.2-62
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Figure 2. The resulting triangulation satisfies the Delauney criterion.4. This vertex data is extracted from whatever 3D data (contours. The Delauney criterion ensures that no vertices lie within the interior of any circumcircles of the TIN triangles (see the following figure).) are defined as layer information within the Configure Elevation Layer dialog box (section titled Configure Elevation Sources on page 2-84).

5 Removing the Floodplain Mapping Results
To remove all floodplain map results from the surface. Scour. above the computed water surface (commonly called freeboard). Surfaces are only available for tracking after their corresponding results have been generated and displayed on the surface.Using the Program
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As the tinning triangulation process proceeds. can scoop out scour holes.5
Tracking Elevations and Depths
Water surface elevations. If there is not enough 3D data contained within the channel bottom. after adding additional ground terrain data.
2. from which you may select the specific 3D surface to track. If necessary.
2. adjacent triangles are compared to see if they satisfy the Delauney criterion. read from data on configured topographical map elevation layers. inserting additional points where these problems occur can quickly resolve these issues. a false dam can be created by the software by using the Delauney criteria. This command displays the Track Flood Surface dialog box.11 Bridge Scour
Bridge scour is the removal of sediment such as sand and rocks from around bridge abutments or piers. However. Negative depths indicate areas outside the edge of water. The water depth for a particular profile. the adjacent edge of the two triangles is swapped (the diagonal of the quadrilateral defined by the two triangles is changed to the other two vertices) in order to satisfy the Delauney criterion. The water surface elevation for a particular profile.
2. compromising the integrity of the bridge. Bridge scour is one of the three main causes of bridge failure.10. and ground terrain elevations may be tracked by clicking River tab > Output panel > Flood Map drop-down > Track Flood Surface. moving the cursor over the topographical map area will display the selected depth or elevation on the AutoCAD command line. caused by swiftly moving water. where 46 of 86 major bridge failures resulted from scour near piers from 1961 to 1976. depths. The result is that long thin triangles are avoided as much a possible. the minimum interior angle of all the triangles is maximized. After selecting a 3D surface.4. click Erase on the Floodplain Map Results dialog box. Available surfaces include: • • • The natural ground surface elevation.10.
. If this occurs. It is the most common cause of highway bridge failure in the United States. If the Delauney criterion is satisfied everywhere on the TIN. It has been estimated that 60% of all bridge failures result from it. turn on the Regenerate Ground Terrain option in the Floodplain Map Results dialog box (page 2-57) to regenerate the ground surface DTM.

Debris might also shift the entire channel around the bridge causing increased water flow and scour in another location. A build-up of debris on the abutment can increase the obstruction area and increase local scour. Over long periods of time. the fill behind abutments may scour. this can result in lowering of the stream bed. The scour report includes all input data. Degradation scour occurs both upstream and downstream from a bridge over large areas. intermediate results. although the foundations of a bridge might not suffer damage. final analysis results. Stream channel instability resulting in river erosion and changing angles-of-attack can contribute to bridge scour. making them susceptible to local scour effects. At bridge openings. A build-up of material can reduce the size of the waterway under a bridge causing contraction scour in the channel. This type of damage typically occurs with singlespan bridges with vertical wall abutments. contraction scour can occur when water accelerates as it flows through an opening that is narrower than the channel upstream from the bridge. During a flooding event. increasing local scour. and analysis narrative—along with placing the computed scour results directly on the bridge within the AutoCAD drawing. Debris can also have a substantial impact on bridge scour in several ways.
.11. variables. changing the angle of attack.0.2-64
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Figure 2.1 Example of damaged support abutment due to scour at the bridge opening (courtesy of USGS)
Water normally flows faster around bridge piers and abutments. equations. Debris can deflect the water flow.
Autodesk River Analysis Bridge Scour Capabilities
The software analyzes a bridge opening for scour and creates a “ready-to-submit” FHWA-accepted bridge scour engineering report in just minutes.

In addition to properly defining the bridge model. such that any user-defined downstream boundary condition does not affect the hydraulic results inside and just upstream of the bridge. pier. a flow distribution of the channel and overbanks is required in order that additional analysis results are available for the scour computations. Once the hydraulic model has been calibrated (if possible). in order to evaluate the long term effects of the bridge on the water surface profile upstream. To perform a bridge scour analysis. The model should also include several cross sections upstream of the bridge. The hydraulic modeling of the bridge should be based on standard. In general. you can enter the design events to be used for the scour analysis.Using the Program
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The scour analysis can account for: • • • • • • • • Bridge skew Pier skew Pier shape Sloping and skewed abutments Soil bed material Armoring of bridge abutments Armoring of bridge piers Contraction. 18 (HEC 18) report. Before performing a bridge scour analysis with the software. accepted bridge modeling procedures. If observed data are available. In addition to this event. The flow distribution analysis provides additional results for each flow slice: • • • • • • Percentage of flow Flow area Wetted perimeter Conveyance Hydraulic depth Average velocity
. the design event for a scour analysis is usually the 100 year (1 percent chance) event. 2001). and abutment scour effects
General Modeling Guidelines
The computation of scour at bridges within the software is based upon the methods outlined in Federal Highway Administration's Hydraulic Engineering Circular No. 18 (FHWA. you should thoroughly review the procedures outlined in the Hydraulic Engineering Circular No. it is recommended that a 500 year (0. This model should include several cross sections downstream from the bridge.2 percent chance) event also be used in order to evaluate the bridge foundation under a major flood. the model should be calibrated to the fullest extent possible. you must first develop a hydraulic model of the river reach containing the bridge to be analyzed.

The number of flow slices the left overbank.
2.e. if a multiple opening roadway crossing needs to be analyzed for scour. so that scour can be computed for each opening separately. and then each bridge opening can be analyzed separately for the contributing flow. which are required for the scour computations. The software does not compute long-term aggradation and degradation. Long term aggradation and degradation should be evaluated prior to performing the bridge opening scour analysis. a HEC-RAS analysis must be performed in order for the flow distribution results be available for the scour computations. you must break the multiple opening model into separate models. but only the above cross sections flow distributions will be used by the bridge scour computations.1
Bridge Scour Calculator
Bridge opening scour is computed by using the Bridge Scour Calculator
. with a maximum number of 45 flow slices defined at a cross section. the next cross section upstream of the bridge. located at a distance such that the flow lines are assumed parallel and the flow has not yet begun to contract due to the bridge constriction)
Flow distributions can be specified at additional cross sections. the bridge scour can then be evaluated. Once the flow distributions have been specified. Procedures for performing long term aggradation and degradation analyses are outlined in the HEC 18 report.. However. After performing the HEC-RAS water surface profile computations for the design events (and computing the flow distribution output).2-66
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
You can control the flow distribution and the number of flow slices at a cross section. The amount of flow through each bridge opening can be determined. and right overbank can be specified. The total scour at a bridge opening roadway crossing is comprised of these components: • • • • Long-term aggradation and degradation Contraction scour Localized scour at piers Localized scour at abutments
The scour computations provided by the software allow you to compute contraction scour and local scour at piers and abutments. A flow distribution must be defined for these cross sections when performing a bridge scour analysis: • • • Bridge opening downstream face cross section Bridge opening upstream face cross section Approach cross section (i.11. These flow distributions provide detailed estimates of the depth and velocity within the cross section.
Analyzing Multiple Opening Roadway Crossings
The software analyzes a single opening bridge for scour. main channel.

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Click River tab > Analysis panel > Bridge Scour Calculator to display the Bridge Scour Calculator dialog box. This dialog box allows you to select the river reach, corresponding bridge opening cross section, and profile to analyze for scour. You can restrict the types of scour analyses to perform, if required. To enter data into the Bridge Scour Calculator, select the appropriate tabs at the top of the dialog box. Each tab provides additional data fields to define the input data necessary to perform a scour analysis of the bridge opening. Most of the input data fields are already populated with the results from HEC-RAS. After you enter the scour data, select the Analysis Results tab to view the results of the scour analysis.

2.11.2

Contraction Scour
Contraction scour occurs when the flow area of a stream is reduced by a natural contraction or a bridge constricting the flow. At a bridge crossing, many factors can contribute to the occurrence of contraction scour. These factors may include: • • • • The main channel naturally contracts as it approaches the bridge opening The road embankments at the approach to the bridge cause all or a portion of the overbank flow to be forced into the main channel The bridge abutments are projecting into the main channel; the bridge piers are blocking a significant portion of the flow area A drop in the downstream tailwater which causes increased velocities inside the bridge

Figure 2.11.2.1 Picture illustrating the impact of contraction scour

There are two forms of contraction scour that can occur depending on how much bed material is already being transported upstream of the bridge contraction reach— defined as live-bed contraction scour and clear-water contraction scour. Live-bed contraction scour occurs when bed material is already being transported into the contracted bridge section from upstream of the approach section (before the contraction reach). Clear-water contraction scour occurs when the bed material sediment transport in the uncontracted approach section is negligible or less than the carrying capacity of the flow.

Contraction Scour Conditions
Four conditions (cases) of contraction scour are commonly encountered: Case 1 Involves overbank flow on a floodplain being forced back to the main channel by the approaches to the bridge. Case 1 conditions include: • The river channel width becomes narrower either due to the bridge abutments projecting into the channel or the bridge being located at a narrowing reach of the river. No contraction of the main channel, but the overbank flow area is completely obstructed by the road embankments. Abutments are set back away from the main channel.

• •

Case 2 Flow is confined to the main channel (i.e., there is no overbank flow). The normal river channel width becomes narrower due to the bridge itself or the bridge site is located at a narrowing reach of the river. Case 3 A relief bridge in the overbank area with little or no bed material transport in the overbank area (i.e., clear-water scour). Case 4 A relief bridge over a secondary stream in the overbank area with bed material transport (similar to Case 1, above).

Contraction Scour Type Determination
To determine if the flow upstream is transporting bed material (i.e., live-bed contraction scour), the software calculates the critical velocity for beginning of motion Vc (for the D50 size of bed material) and compares it with the mean velocity V of the flow in the main channel or overbank area upstream of the bridge at the approach section. If the critical velocity of the bed material is greater than the mean velocity at the approach section (Vc > V), then clear-water contraction scour is assumed. If the critical velocity of the bed material is less than the mean velocity at the approach section (Vc < V), then live-bed contraction scour is assumed. You have the option of forcing the software to calculate contraction scour by the live-bed or clear-water contraction scour equation, regardless of the results from the comparison.

Entering Contraction Scour Data
You enter contraction scour data on the Contraction tab of the Bridge Scour Calculator dialog box. All of the input variables, except D50 and K1 are obtained automatically from the HEC-RAS output results. You can change any input variable to whatever value is thought to be appropriate. To compute contraction scour, you are only required to enter the D50 (mean size fraction of the bed material) and an assumed water temperature (to compute the K1 factor).

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The input data for the Contraction tab is detailed below. Note that contraction scour is computed separately for the left overbank, main channel, and right overbank. Therefore, there are three columns of data for defining the necessary input. However, if there is not any left or right overbank flow in the model results, then the corresponding dialog box fields will be accordingly empty. Approach Cross Section This list is used to select the cross section that is assumed to act as the approach cross section to the bridge opening. The approach cross section should be located at a point upstream of the bridge just before the flow begins to contract due to the constriction of the bridge opening. The software assumes that the approach cross section is the next upstream cross section from the bridge's upstream face cross section. If this is not the case, you can select a different cross section to be used as the approach cross section.

Figure 2.11.2.2 Location of approach cross section

Scour Equation You have the option to allow the software to decide whether to use the live-bed or clear-water contraction scour equations, or to select a specific equation. If you select the Default option (software selects which equation is most appropriate), the software must compute Vc (the critical velocity that will transport bed material finer than D50). If the average velocity at the approach cross section is greater than Vc, the software uses the live-bed contraction scour equation. Otherwise, the clear-water contraction scour equation will be used. Y1 The average depth (hydraulic depth) in the left overbank, main channel, and the right overbank, at the approach cross-section. This computed value can be overridden.

taken at the interior cross section at the upstream side of the bridge. water temperature. Water Temperature Assumed water temperature. This computed value can be overridden. and right overbank at the approach cross section. This field is read-only. This computed value can be overridden. The software can compute a value for K1 or you can specify one. taken at the approach cross section. These particle sizes must be specified. Fall Velocity (w) Computed fall velocity of the specified D50 bed material. W2 The top width of the active flow area (not including ineffective flow area). W1 The top width of the active flow area (not including ineffective flow area). at the approach section. and right overbank. Energy Slope (S1) Computed energy slope at the approach cross section. This computed value can be overridden. Y0 The average depth in the left overbank. main channel. To have the software compute a K1 value. This computed value can be overridden. for the left overbank. in ft/sec. Shear Velocity (V*) Computed shear velocity at the approach cross section. in ft/sec. main channel. This computed value can be overridden. and right overbank. Q1 The flow in the left overbank. Q2 The flow in the left overbank. at the interior cross section at the upstream side of the bridge.2-70
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V1 The average velocity of flow in the left overbank. D50 Particle Size The bed material particle size of which 50% are smaller. and the right overbank. K1 An exponent for the live-bed contraction scour equation that accounts for the mode of bed material transport. at the interior cross section at the upstream side of the bridge. This field is read-only. click Compute. main channel. and right overbank. main channel. This computed value can be overridden.
. main channel. in ft/ft (or m/m). and the fall velocity (w) of the D50 bed material. in degrees Fahrenheit. K1 is a function of the energy slope (S1) at the approach section. the shear velocity (V*) at the approach section. This computed value can be overridden.

11. Flow through relief bridges or over approaching roadway embankments can reduce the flow and contraction scour in the main channel bridge opening. Large substructure elements (i.
• • • • •
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Contraction Scour Observations
The following observations should be considered when analyzing a bridge opening for potential contraction scour. The horseshoe vortex removes material from the base of the pier. Eventually an equilibrium between bed material inflow and outflow is reached.e. pile groups) can increase contraction scour significantly. As the depth of scour increases.. If there is no overbank flow.1 Illustration of pier scour mechanics
. which can increase scour dramatically. the magnitude of the horseshoe vortex decreases. • Significant contraction scour can occur if overbank flows (the portion of the high-flow above and outside of the banks of the main channel) are captured by roadway approach embankments and forced through the bridge opening.11. piers. creating a scour hole.
Figure 2. and the scour hole ceases to grow. pile caps.3.3
Pier Scour
Pier scour occurs due to the acceleration of flow around the pier and the formation of flow vortices (known as the horseshoe vortex). only a change in the effective main channel width (including bridge piers in the flow) will influence live-bed contraction scour. thereby reducing the rate at which material is removed from the scour hole. Submergence of the bridge superstructure causes pressure flow (vertical contraction scour). Deep contraction scour is possible at relief bridges located in the overbank.

Scour Equation Pier scour can be computed by either the Colorado State University (CSU) equation (Richardson. or the local velocity and depth at each pier for the calculation of the pier scour.
. 1990) or the Froehlich (1988) equation (the Froehlich equation is not included in the HEC 18 report). All of the input variables. You can change any input variable to whatever value is thought to be appropriate. In addition to the CSU equation. David Froehlich (1991) has also been added as an alternative pier scour equation. The input data for the Pier tab is described below. an equation developed by Dr. Velocity & Depth This list provides the option to use the maximum velocity and depth in the main channel. 1990) for the computation of pier scour under both live-bed and clear-water conditions.2-72
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The factors that affect the depth of local scour at a pier are: • • • • • • • • • Velocity of the flow just upstream of the pier Flow depth Pier width Length of the pier (if skewed to the flow) Size and gradation of bed material Angle of attack of approach flow Shape of the pier Bed configuration Formation of ice jams and debris
The HEC 18 report recommends the use of the Colorado State University (CSU) equation (Richardson. the angle of attack for flow hitting the piers.
Entering Pier Scour Data
Enter pier scour data on the Pier tab of the Bridge Scour Calculator dialog box. In general. the maximum velocity and depth are used to account for the potential of the main channel thalweg to migrate back and forth within the bridge opening. The CSU equation is the default. except the pier nose shape (K1). The migration of the main channel thalweg could cause the maximum potential scour to occur at any one of the bridge piers. and a D95 size fraction for the bed material are obtained automatically from the HEC-RAS output results. The Froehlich equation is not recommended in the HEC 18 report. but has been shown to compare well with observed data. the condition of the bed (K3). et al. The CSU equation is the default pier scour equation.

You can change the value for all piers or any individual pier. You can select between the following pier shapes: • • • • • Square nose Round nose Circular cylinder Group of cylinders Sharp nose (triangular)
When you select a shape. or a different shape can be entered for each pier. This is the default option. or is applicable to that pier. Local V1 Y1 If you select this option.
. Optionally. You can change this value. You can set the pier nose shape for all piers. D50 Particle Size Median diameter of the bed material of which 50 percent are smaller. will be displayed in each of the data fields. You can then enter any missing information for that pier. When Apply to All Piers is selected. When a specific pier is selected. based on what was entered for the left overbank. the K1 factor for the CSU equation and the Phi factor for the Froehlich equation are automatically set. the software finds the maximum velocity and depth located in the cross section just upstream and outside of the bridge. The maximum velocity (V1) and depth (Y1) will then be used for all of the piers. main channel. you can select a specific pier from this drop down list. only the portion of the data that should be applied to all of the piers. You do not have to enter all of the data in this mode. This field is read-only. Pier # This list specifies how the data can be entered. any data that has already been entered. the software finds the velocity (V1) and depth (Y1) at the cross section just upstream and outside of the bridge that corresponds to the centerline stationing of each of the piers. Pier Width (a) This field is used to enter the width of the pier (measured perpendicular to the flow direction). This value is automatically filled-in for each pier. Pier Shape This list specifies the pier nose (upstream end) shape. the pier data entered will be applied to all of the piers. The software automatically puts a value in this field based on the bridge input data. This is taken from the flow distribution output for the cross section just upstream from the bridge. Froude Number (Fr1) Froude Number directly upstream of the pier. or change any data that was already set. and right overbank on the Contraction scour tab.Using the Program
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Maximum V1 Y1 If you select this option. The software uses the flow distribution output to obtain these values.

You can change this value directly for each or all piers. This factor is automatically calculated once you enter the pier width. then the angle would be entered as zero. used in the CSU equation. The value is taken from the flow distribution output at the cross section just upstream and outside of the bridge. You can change the length for all piers or each individual pier. then this field will show the maximum velocity of water in the cross section for all piers.2-74
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Y1 This field displays the depth of water just upstream of each pier. Pier Length (L) This field represents the length of the pier through the bridge. You can change this value directly for each or all piers.0. The value is taken from the flow distribution output at the cross section just upstream and outside of the bridge. This length is used in determining the magnitude of the K2 factor. If you have specified Maximum V1 Y1 as the Velocity & Depth. used in the CSU equation. V1 This field displays the average velocity just upstream of each individual pier. This factor is automatically set when you select a pier nose shape. Pier Skew Angle This field is used to enter the angle of attack of the flow approaching the pier. K1 Correction factor for pier nose shape. D95 Particle Size The median size of the bed material of which 95 percent is finer. and the angle of attack. If you have specified Maximum V1 Y1 as the Velocity & Depth. The D95 size fraction is used in the computation of the K4 factor. You can override the calculated value. used in the CSU equation. the software automatically sets a value for the K2 coefficient. The field is automatically set by the software to equal the width of the bridge. You can select from the following bed conditions: • • • • • Clear-water scour Plane bed and antidune flow Small dunes Medium dunes Large dunes
. then this field will show the maximum depth of water in the cross section for each pier. the pier length. When the angle is > 5 degrees. then that angle should be entered as a positive value in degrees. and must be defined. K2 Correction factor for angle of attack of the flow on the pier. If the flow direction upstream of the pier is perpendicular to the pier nose. K1 is set to 1. When an angle is entered. You can override the selected value. K3 Correction factor for bed condition. If the flow is approaching the pier nose at an angle.

006 feet (0.002 m) and the D95 is greater than 0. angle. This factor should be manually calculated and is based on the pier width. You can override the selected value. This factor is automatically set when you select a pier nose shape. Phi Correction Correction factor for pier nose shape. The K4 factor is used in the CSU equation. and is a function of D50. and the depth of water just upstream of the pier. This factor is specific to Froehlich's equation.
. This factor is only applied when the D50 of the bed material is greater than 0. shape.06 feet (0.Using the Program
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K4 This factor is used to decrease scour depths in order to account for armoring of the scour hole. Projected Width (a’) The projected pier width with respect to the direction of the flow. This factor is automatically calculated by the software. pier width. D95.02 m). used in the Froehlich equation. and length.

Maximum expected pier scour depth ranges from 2. Shape of the pier has an effect on scour: • • A streamlined upstream end reduces the strength of the horseshoe vortex reducing scour depth. A streamlined downstream end reduces the strength of the wake vortices. • • • Width of pier has a direct effect on the depth of scour.2-76
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Pier Scour Observations
The following observations should be considered when analyzing a bridge opening for potential pier scour. change the shape of piers. clay.
. Ice and debris can increase the width of the piers. • • • • The effect of cohesion is to increase the time it takes to reach the ultimate scour depth. the maximum depth of scour is measured in hours. Fine streambed sediments (silt and clay) will have scour depths as deep as sandbed streams. Velocity of the approaching flow increases the scour depth (faster flow produces deeper scour).
• •
In sand-bed channels. etc. however.4 to 3 times the pier width for circular or round-nosed piers aligned with the flow. With cohesive streambed materials (silt.
2. and forms a vertical wake vortex at the downstream end of the abutment. The obstruction of the flow forms a horizontal vortex starting at the upstream end of the abutment and running along the toe of the abutment. or even years to reach the maximum scour depth. and cause the flow to plunge downward against the streambed and increase pier scour. rock.
• • •
Square-nose pier will have a maximum scour depth about 20 percent larger than a sharp-nose pier and 10 percent larger than a cylinder or round-nose pier.) it may take days. wider piers produce deeper scour than narrow piers under the same conditions. sandstone.11. an angle of attack of the flow to the pier has a large effect on local scour.4
Abutment Scour
Local scour occurs at bridge abutments when the abutment obstructs the flow. Length of the pier has no appreciable effect on scour depth if the pier is aligned with the flow. even if bonded by cohesion. months. Shape of the pier nose has no effect on the magnitude of the scour when the angle of the attack is greater than about 5 degrees.

The selection is based on computing a factor of the embankment length divided by the approach depth.
. You can change any input variable to whatever value is thought to be appropriate. Abutment scour is computed separately for the left and right abutments. This list allows you to select from the following equations: • Default mode • HIRE equation • Froehlich equation When the Default mode is selected. 1990). The input data for the Abutment tab is described below. 1989). If this factor is greater that 25.1 Illustration of abutment scour mechanics
The HEC 18 report recommends two equations for the computation of live-bed abutment scour.4. 1990) or Froehlich's equation (Froehlich. the software automatically uses the HIRE equation. If the factor is equal to or less than 25. the software automatically uses the Froehlich equation. 1989). the software chooses the equation that is the most applicable to the situation. When the wetted embankment length (L) divided by the approach flow depth (Y1) is greater than 25. All of the input variables.Using the Program
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Figure 2.11. except abutment type are obtained automatically from the HEC-RAS output results. Scour Equation Abutment scour can be computed by either the HIRE equation (Richardson. the HEC 18 report suggests using the HIRE equation (Richardson. the HEC 18 report suggests using an equation by Froehlich (Froehlich.
Entering Abutment Scour Data
Enter abutment scour data on the Abutment tab of the Bridge Scour Calculator dialog box. When the wetted embankment length divided by the approach depth is less than or equal to 25.

The left embankment length is computed as the stationing of the left abutment toe (projected up to the approach cross section) minus the station of the left extent of the active water surface in the approach cross section.. Abutment Flow Angle This field is used to enter the angle of attack of the flow against the abutment. Depth of Water at Toe (Y1) This value is the computed depth of water at the station of the toe of the embankment. at the approach cross section. Abutment Shape (K1) This value represents a correction factor accounting for abutment shape. A value of 90 degrees should be entered for abutments that are perpendicular to the flow (i. Abutment Length Length of the abutment and road embankment that is obstructing the flow. The right embankment length is computed as the stationing of the right extent of the active water surface minus the stationing of the toe of the right abutment (projected up to the approach cross section). at the cross section just upstream of the bridge. This skew angle is used in computing the K2 factor. where the toe of the abutment intersects the natural ground. The location for the abutment toe stationing can be changed directly in this field.e. This value can also be changed. The software automatically selects a value for this stationing at the point where the road embankment and/or abutment data intersects the natural ground crosssection data. The location for this stationing can be changed directly in this field. The location of the toe of the abutment is based on where the roadway embankment intersects the natural ground. The value is computed by the software as the elevation of the water surface minus the elevation of the ground at the abutment toe stationing. This value is used in the HIRE equation.2-78
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Toe Station at Bridge XS This field is used to define the stationing in the bridge upstream internal cross section. If you do not like the stationing that the model picks. These lengths can be changed directly. A value greater than 90 degrees should be entered if the abutments are pointing in the upstream direction. You can choose among the following abutment shapes: • Vertical abutments • Vertical abutments with wing walls • Spill-through abutments
. A value less than 90 degrees should be entered if the abutment is pointing in the downstream direction. normal situation). Toe Station at Approach XS This field is used to define the stationing in the approach cross section. The software automatically computes this value for both the left and right embankments. you can override it by entering your own value. based on projecting the abutment toe station onto the approach cross section. This stationing is very important because the hydraulic variables used in the abutment scour computations will be obtained from the flow distribution output at this cross section stationing.

This value is computed by projecting the stationing of the abutment toe up to the approach cross section. this factor increases from a value of one. This value is automatically computed by the software once you enter an abutment length and a skew angle. Abutment Projected Length (L’) The length of the abutment (embankment) projected normal to the flow (projected up to the approach cross section).Using the Program
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Skew Correction Factor (K2) Correction factor for angle of attack of the flow on the abutments. These percentages are multiplied by the total flow to obtain the discharge blocked by each embankment.
. These values can be overridden. This factor is automatically computed by the software. These values can be overridden. As the skew angle becomes greater than 90 degrees. This value is then computed as the area divided by the top width. From the flow distribution output. Abutment Toe Velocity (V1) The velocity at the toe of the abutment. Abutment Average Flow Depth (Ya) The average depth of flow (hydraulic depth) that is blocked by the embankment at the approach cross section. the software calculates the area and top width left of the left abutment toe and right of the right abutment toe. These values can be overridden. This value can be overridden. As the skew angle becomes less than 90 degrees. This value is computed by projecting the stationing of the abutment toe onto the approach cross-section. This value can be overridden. Abutment Flow Area (Ae) The flow area that is obstructed by the abutment and embankment at the approach cross section. the software calculates the percentage of flow left of the left abutment toe and right of the right abutment toe. taken from the cross section just upstream and outside of the bridge. From the flow distribution output. This velocity is obtained by finding the velocity in the flow distribution output at the corresponding cross section stationing of the abutment toe. This value is computed by projecting the stationing of the abutment toe onto the approach cross-section. Abutment Flow (Qe) The flow obstructed by the abutment and embankment at the approach cross section. From the flow distribution output. this value becomes less than one. This field is read-only. the software calculates the area left of the left abutment toe and right of the right abutment toe.

click Erase. Therefore. The top width of the local scour hole around a pier is computed as 2. click Place. Abutment scour will be most severe where the approach roadway embankment leading to the abutment obstructs a significant amount of overbank flow. Scour can occur along the upstream portion of the abutment due to the horizontal vortex and at the downstream end of the abutment as the flow expands through the bridge opening. Therefore. • • • • Potential for lateral channel migration. Riprap and guide banks may protect an abutment from failure. To automatically generate a report within Microsoft Word. the total top width of the scour hole at a pier is plotted as (4. If changes are made to the scour input data. This tab displays the scour analysis results for the defined data.0 ys around each side of the abutment toe.
.
• • •
2.0 ys. long-term degradation. To export the report to an RTF (Rich Text Format) cross-platform document interchange file. click Report. contraction scour.11. The local pier and abutment scour are then added to the contraction scour. select the Analysis Results tab.2-80
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Abutment Scour Observations
The following observations should be considered when analyzing a bridge opening for potential abutment scour. The contraction scour is plotted as a separate line below the existing conditions cross section data. click Recompute and the Bridge Scour Calculator will recompute the analysis results. The top width of the local scour hole at abutments is plotted as 2. and local scour at each individual pier and abutment. The software plots both contraction scour and total local scour.0 ys + a).0 ys to each side of the pier (ys is the scour depth). the total top width of the scour hole at abutments is plotted as 4. Vertical wall abutment without wingwalls can have twice the scour depth as a spill-through (sloping) abutment. and contraction scour should be considered when monitoring for abutment scour. To place the scour results on the cross section containing the bridge structure.5
Scour Analysis Results
Once the scour input data has been defined. To erase previously placed scour results from the bridge cross section. Abutment scour will increase if the abutment (embankment) is skewed in an upstream direction (into the flow). click Export. Abutment scour will decrease if the abutment (embankment) is skewed in a downstream direction (away from the flow).
Total Scour Computations
The total depth of scour is a combination of long-term bed elevation changes. and then plotted as total scour depths.

the software reverts to its default values. which is contained in the user directory. as they provide a smoother transition through a bridge opening. A number of physical additions to the abutments of bridges can help prevent scour.1
Configure Cross Section Views
To access the Configure Section Views dialog box. Drawing specific configurations are stored in the drawing itself. Changing any of these values causes all cross section views in the drawing to be regenerated. and vanes are river training structures that change stream hydraulics to mitigate undesirable erosion or deposits.11.CFG.
. Station: Scale Defines how many feet per inch (or meters per meter) are to be represented by the scaled cross section view horizontal station axis. The insertion of piles or deeper footings is also used to help strengthen bridges.
Grid Axes
These entries define how the cross section view station and elevation axes are to be sized and scaled when a new cross section view is added. groynes. barbs.
2.12 Program Configuration
Most of the software's non-drawing specific (general) configurations are stored in a configuration file called River.Using the Program
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2. This eliminates abrupt corners that cause turbulent areas. such as the installation of gabions and stone pitching upstream from the foundation. The XS Grids tab of the Configure Section Views dialog box is used to specify how new cross section views are drawn. click River tab > Input panel > Section Geometry drop-down > Configure Section Views.12. Trapezoidal-shaped channels through a bridge can significantly decrease local scour depths compared to vertical wall abutments. or how an existing cross section view is resized. Spur dikes.
Cross Section ID: Increment
Specifies the increment for the automatically generated cross section ID number. If this file is deleted or if you receive a newer version of software.6
Bridge Scour Prevention
Riprap remains the most common countermeasure used to prevent scour at bridge abutments. The software's configuration settings are described in the following sections. the following paragraphs describe the options on the XS Grids tab. They are usually used on unstable stream channels to help redirect stream flow to more desirable locations through the bridge. The addition of sheet piles or interlocking prefabricated concrete blocks can also offer protection.
2.

The software automatically labels as many of the station tick marks as possible. Elevation: Tick Interval Defines the interval (in feet or meters) at which tick marks and grid lines will be drawn perpendicular to the cross section view vertical elevation axis.
Resize Options
Specifies how cross section view is resized when you click River tab > Input panel > Section Geometry drop-down > Resize Section Views. a station tick interval of 50 means that a tick mark and grid line is drawn every 50 feet (or meters) along the station axis. Therefore. if this round off value is 100. care should be exercised when locating the grid array on the AutoCAD drawing. locating the cross section grid array too far away from the topographical map may cause excessive regenerations to occur when zooming between a surface and a cross section view.
Grid Array Pattern
These entries define the location and the array pattern used to lay out the cross section views. This entry is used to determine at what elevation values a newly created cross section view will start and end. an elevation tick interval of 10 means that a tick mark and grid line is drawn every 10 feet (or meters) along the elevation axis. Elevation: Round Off This data entry is used when generate new grid is selected as the grid generation method. For example. both station and elevation axes are resized.
. it is recommended that you locate the cross section grid array in an area on the drawing that is unlikely to be used. By default. For example. The cross section views are laid out in an evenly spaced array.2-82
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Station: Tick Interval Defines the interval (in feet or meters) at which tick marks and grid lines is drawn perpendicular to the cross section view horizontal station axis. to include the length from stations 140 to 340. this array could occupy a large amount of drawing space. Depending on the size of the largest cross section view and the total number of cross section views. a grid station axis with a specified starting station of 140 and a station axis length of 200 would is generated from station 100 to station 400. Therefore. However. but labels whose text would appear on top of a neighboring label are skipped. This entry is used to determine at what station values a newly created cross section view will start and end. For example. Station: Round Off This data entry is used when generate new grid is selected as the grid generation method. Elevation: Scale Defines how many feet per inch (or meters per meter) are to be represented by the scaled cross section view vertical elevation axis.

Text and Symbol Sizes
This section is used to define the sizes of the text and symbols used on the cross section views. Columns Specifies the number of columns to use in the generated grid array. these spacing values will be automatically calculated during importation of a HEC-RAS or HEC-2 data input file. simply re-specify the array layout pattern and location. neighboring views may overlap. ID Text Defines the cross section ID text size (in drawing units) displayed under the cross section view. X Grid Spacing Y Grid Spacing Specify for the grid array. Click Defaults to set these entries back to their default values. X Layout Point Y Layout Point Specify the X and Y coordinates of the lower left corner of the cross section grid array. When a row in the array contains this many cross section grids. Click Compute to automatically calculate grid spacing values to prevent currently existing cross section views from overlapping. Manning’s Roughness Text Defines the Manning’s roughness text size (in drawing units) displayed on the cross section view. Overbank Symbol Defines the overbank symbol size (in drawing units) displayed on the cross section view. Click < to select the array layout point from the AutoCAD drawing screen.
. If the cross section views are spaced too closely. If Compute on Import is selected. Tick Mark Text Defines the tick mark text size (in drawing units) displayed on the cross section view. a new row is started. The software will then regenerate the cross section grid array. Description Text Defines the cross section description text size (in drawing units) displayed under the cross section view. some of these grid arrays could overlap.Using the Program
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If you find that the cross section grid array layout pattern needs to be adjusted or relocated. the number of drawing units between each row and column for the cross section view insert locations. preventing cross section view overlap. If the cross section grid array is placed too close to the profile grid array or topographical map.

2
Configure Elevation Sources
When entering cross section ground geometry using the 3D or 2D Map methods.12. you will be prompted to configure the status. and polyfaces found on these layers or surfaces will be used in building a 3D terrain model for computing the water surface intersection. click River tab > Output panel > Profile Views drop-down > Configure Profile Views. The following paragraphs describe the options on the Configure Profile Views dialog box.
Grid Axes
The following entries are used to specify how the profile grid station and elevation axes are sized and scaled when a new profile View is added. faces. but only for layers or surfaces that have been configured as valid elevation sources. polylines. Any entities found on this layer or surface will be ignored when entering ground geometry. Any points. click River tab > Input panel > Create Section drop-down > Section Elevation Data Source. Any points. polylines. lines. Use The layer or surface contains ground geometry information. Any points. lines. polylines. If an entity is found on a layer or surface whose status has not previously been defined. Ignore The layer or surface does not contain ground geometry information. 3D polyfaces.
Interpolated Edge of Water
The software will use the layers or surfaces identified as Use for computing the interpolated edge of water. If a possible ground geometry information is found on this layer or surface.2-84
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
2. or polyfaces found on this layer or surface will be read for 2D or 3D elevations when entering ground geometry. you will be prompted to configure the layer or surface status.
2. The Configure Profile Views dialog box is used to specify how a new profile view is drawn. To configure the elevation data sources. as well as each layer's known elevation status. which can be one of the three following types: Verify The layer or surface is not yet configured. 3D faces. the software will search for any elevation data on the topographical map which intersect the cross section line entered. The Section Elevation Data Source dialog box lists all layers and surfaces defined for the current drawing (except layers used by the software).3
Configure Profile Views
To configure profile views.12. or how an existing profile
. or Civil 3D surfaces intersected will be examined for possible elevation data. faces. lines.

Depending on the size of the largest profile view and the total number of profile views. a station tick interval of 200 means that a tick mark and grid line is drawn every 200 feet (or meters) along the river station axis.
Grid Array Pattern
These entries define the location and the pattern used to layout the profile views. For example. Elevation: Scale Defines how many feet per inch (or meters per meter) are to be represented by the scaled profile view vertical axis. Station: Roundoff Determines at what station values a newly created profile view will start and end. Elevation: Roundoff Determines at what elevation values a newly created profile view will start and end. it is recommended that you locate the profile grid array in an area on the drawing that is unlikely to be used. an elevation tick interval of 10 means that a tick mark and grid line will be drawn every 10 feet (or meters) along the elevation axis. but labels whose text would appear on top of a neighboring label are skipped. a grid with a specified starting station of 140 and a station axis length of 200 would be generated from station 100 to station 400. For example. For example. to include the length from stations 140 to 340. if the roundoff value were 100.
. Therefore. Station: Tick Interval Defines the interval (in feet or meters) at which tick marks and grid lines will be drawn perpendicular to the profile view horizontal axis. Station: Scale Defines how many feet per inch (or meters per meter) are to be represented by the scaled profile view horizontal axis. The profile views are laid out in an evenly spaced array. this array could occupy a large amount of drawing space.Using the Program
2-85
view is resized. Changing any of these values causes all profile views in the drawing to be regenerated. The software automatically labels as many of the station tick marks as possible. Elevation: Tick Interval Defines the interval (in feet or meters) at which tick marks and grid lines will be drawn perpendicular to the profile view vertical axis.

a new row is started.0 causes no adjustment to be made. Click Compute to automatically calculate grid spacing values to prevent currently existing profile views from overlapping. Tick Mark Text Defines the tick mark text size (in drawing units) displayed on the profile view. roadway deck symbols.
. low chord. X: Grid Spacing Y: Grid Spacing Specify the number of drawing units between each row and column for the profile grid insert locations. Bridge/Culvert/Roadway Scale Adjusts the horizontal size of the symbols used to draw the bridge opening invert. X: Layout Point Y: Layout Point Specify the X and Y coordinates of the lower left corner of the profile grid array. A value of 0. simply re-specify the array layout pattern and location. neighboring views may overlap. A value of 1.0 causes no adjustment to be made. If the profile grid array is placed too close to the cross section grid array. Description Text Defines the profile description text size (in drawing units) displayed under the profile view. horizontally. Line Symbol Scale Adjusts the size of the symbols drawn on the computed water surface. energy grade line. The software regenerates the profile grid array. or topographical map. A value of 0. Profile ID Text Defines the profile ID text size (in drawing units) displayed on the profile view. A value of 1.5 makes these symbols 50% smaller. Click Pick to select the array layout from the AutoCAD drawing screen.
Text and Symbol Sizes
This section is used to define the size of the text and symbols used on the profile views. Columns Specifies the number of columns to use in the generated grid array.5 makes these symbols 50% shorter. Click Defaults to set these entries back to their default values. ID Text Defines the profile ID text size (in drawing units) displayed under the profile view. some of these grid arrays could overlap. If the profile views are spaced too closely.2-86
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
If you find that the profile grid array layout pattern needs to be adjusted or relocated. and other lines displayed on the profile grid. When a row in the array contains this many profile views.

Contour Interval Specifies the initial elevation contour interval to use when digitizing a cross section from an on-screen 2D topographical map or paper topographical map. Once digitizing has started. This entry is ignored when digitizing from a paper topographical map.4
Configure Topographical Map
Configure the software for digitizing cross sections from on-screen 3D and 2D topographical maps and from paper topographical maps. To configure the topographical map. This entry is ignored when digitizing from an on-screen 3D topographical map.
2. These options need to be completed only when first setting up a drawing that uses a topographical map. This scaling factor defaults to 1 foot (or meter) per drawing unit.Using the Program
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Resize Options
Specifies how a profile grid is resized when you click River tab > Output panel > Profile Views drop-down > Resize Profile Views. The following paragraphs describe the Topographical Map configuration options. and it should be changed if the topographical map's elevation scaling factor is different. Map Text Height Specifies the text height size (in drawing units) of the cross section ID labels that are placed. this elevation contour interval can be adjusted using the Page Up and Page Down keys. This entry does not apply when digitizing from an on-screen 2D topographical map or paper topographical map. On the Configure Section Views dialog box. 2D/3D Map Scale Specifies the X and Y coordinate scaling factor when using an on-screen 2D or 3D topographical map.
Converting Between Metric and English Units
There are times when you may run into map data that has different unit bases for X-Y data and elevation data. This entry should match the contour elevation step represented in the topographical map being used. along with the digitized cross section. and should be changed if the topographical map is drawn at a different scaling factor. 3D Elevation Scale Specifies the elevation scaling factor to use when digitizing cross sections from an on-screen 3D topographical map. only the Elevation axis is resized. This scaling factor defaults to 1 foot (or meter) per drawing unit. For example. click the General tab. on the on-screen 3D and 2D topographical maps. By default. This entry is ignored when digitizing from a paper topographical map. USGS DEM files have their X-Y coordinate data
. click River tab > Input panel > Section Geometry drop-down > Configure Section Views.12.

a scale factor of 3.3048 should be used. switching to a different unit of measurement simply changes the data prompts to reference this new unit base.2-88
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
in UTM (Universal Transverse Mercator) units (which are metric coordinates).12.12.3048 should be specified for the 3D Elevation Scale entry.
Changing a Drawing’s Precision
Click Update to update the station and elevation precision for the entire drawing. saving the drawing automatically saves these settings as well. The 2D/3D Map Scale and 3D Elevation Scale configuration entries can be used to specify unit conversion factors so that the cross section geometry that is cut from topographical map is in the same unit base for both X-Y and elevation data. On the Configure Section Views dialog box. a scale factor of 0. a scale factor of 3. Therefore. but instead are saved in the software’s configuration file.5
Configure Elevation Precision
To configure the precision of River Analysis elevation units.28084 should be specified for the 2D/3D Map Scale entry. This precision is also used in displaying any of these data values in dialog boxes.
2. However.
Note
Once data is entered in a particular unit of measurement. Elevation Decimal Input Precision Specifies the desired decimal precision to be used for all data digitized from the screen or tablet.6
Saving Configuration Settings
The software stores many settings along with the AutoCAD drawing that are specific to the model being analyzed. Decreasing a drawing’s precision truncates decimal digits from the station and elevation data values—it does not round the values. to create cross sections in meters. to create cross sections in feet from a USGS DEM contour map.
. a scale factor of 0.
2. Similarly. It does not convert the data. there are many general settings that are not saved with the drawing. whereas the elevation component of the DEM data is often in feet. To convert feet to meters. To convert meters to feet. Therefore.28084 should be used. which is also automatically saved when the drawing is saved. click River tab > Input panel > Section Geometry drop-down > Configure Section Views. click the General tab.

Generally. Subcritical should be selected. click River tab > Create Reach Data panel > Flows. Profiles Select the profiles that you want to analyze. You can switch between subcritical. When the Water Surface Elevation condition is selected. the profile computations start at a known water surface elevation. the profile computations start at a calculated normal depth.
. then boundary conditions must be specified at both the downstream and upstream ends of the river.Input Descriptions
3-1
C H A P T E R
Input Descriptions
3. or Mixed profiles. In the Flows dialog box. specify the following parameters: Reach Specify the reach number that you want to analyze. and mixed starting profile conditions. If a supercritical flow regime is to be calculated. supercritical. Downstream Condition Upstream Condition Specify the computation method to be used downstream and upstream. When the Normal Depth condition is selected. without losing any previously defined data. Profile Type Specify whether the model is to compute either Subcritical. When both subcritical and supercritical conditions exist in a model. If a mixed flow regime calculation is to be performed. In a subcritical flow regime. the profile computations start at critical depth. boundary conditions are only specified at the upstream end of the river. To access the Flows dialog box. When the Critical Depth condition is selected. This water surface elevation must be specified.
The Flows dialog box allows you to specify up to fifteen different flow profiles for which the software provides solutions. Supercritical. boundary conditions are only specified at the downstream end of the river. then Mixed should be selected.1 Flow Information
3
This chapter provides complete descriptions of the HEC-RAS data input commands.

Selecting Subcritical. HEC-RAS first computes the water surface profile for the natural channel (without any encroachments) using the first specified discharge and then computes profiles using the specified encroachment for all subsequent discharges. Generally. a mixed profile type can be selected and water surface profile will always be computed correctly. supercritical. in steep reach regions. you must select a profile type (i. the profile computations are based on a user-defined rating curve.
Switching Between Profile Types
You can define different starting profile conditions for subcritical.
User Selection of Profile Analyses
Autodesk River Analysis allows you to specify up to 15 separate profiles in the Flows dialog box and then analyze only selected profiles. subcritical.
Floodplain Encroachment Studies
If floodplain encroachments are specified. and mixed profiles.e. channel bed slopes with greater than a 1% grade (i. When a subcritical profile is specified. This can be used to aid in selecting the appropriate profile type when initially defining a HEC-RAS model.
. computations are run in both directions and the appropriate (correct) water surface elevation is automatically selected. encroachment analyses require that at least two profiles be specified. Usually a subcritical profile type should be selected. supercritical.. However. or Mixed for the Profile Type allows you to define completely different starting profile conditions. computations start at the upstream cross section of the channel and proceed downstream. However. a subcritical profile computations may completely or partially fail for the entire reach of river being modeled. each containing different specified values for the displayed data entries. when in doubt.e. computations originate at the downstream cross section of the channel and then proceed upstream. Therefore.. When a supercritical profile is specified. Switching between profile types will not lose previously defined data. This will cause HEC-RAS to assume critical depth at locations where the water surface profile analysis failed. and all subsequent profiles will then be encroached. The first profile will be the natural (unencroached) profile. or mixed). a 1 ft rise in a 100 ft run) will be supercritical and bed slopes with less than a 1% grade will be subcritical. Supercritical.
Selection of Profile Type
When initially defining a HEC-RAS water surface profile model. When a mixed profile is specified.3-2
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
When the Rating Curve condition is selected.

You can use the calculator to compute the normal depth elevation at the most downstream cross section (if computing a subcritical profile) or most upstream cross section (if computing a supercritical profile).
3. If the solution at minimum error is less than this value. the solution with the minimum error (assumed minus computed water surface) is saved. then the software issues a warning and defaults the solution to critical depth. issues a warning. As the software attempts to balance the energy equation. The software uses pre-defined default values for these entries. Critical Depth Calculation Tolerance Specifies the convergence tolerance used in computing the critical depth.
. When the computed difference is less than the specified tolerance. the software assumes that it has a valid numerical solution. To access the Analysis Options dialog box. The computations then proceed from there.2
Analysis Options
The Analysis Options dialog box allows you to specify the computational job parameters for the software. Maximum Number of Iterations Specifies the maximum number of iterations the software makes when attempting to balance the water surface calculations.Input Descriptions
3-3
Water Surface Elevation Estimate
The Hydraulic Calculator allows you to compute the normal depth elevation corresponding to a specified discharge at the currently selected cross section. the minimum error solution is checked against the maximum difference tolerance. If the solution at minimum error is greater than the maximum difference tolerance. The Analysis Options dialog box data entries can generally be left blank. This value can then be entered as the starting water surface elevation in the Flows dialog box. In the Analysis Options dialog box. If the software goes to the maximum number of iterations without meeting the specified calculation tolerance. Maximum Difference Tolerance Specifies the convergence tolerance used during the balance of the energy equation. The Hydraulic Calculator is available from the River tab > Analysis panel. click River tab > Analysis panel > Analysis Options. and then proceeds with the calculations. then the software uses the minimum error solution as the answer. specify the following parameters: Water Surface Calculation Tolerance Specifies the calculation convergence tolerance to be used in comparing against the difference between the computed and assumed water surface elevations.

The resultant is then used as a flow tolerance for the balance of weir flow and flow through the structure. This factor is multiplied by the total flow. Maximum Difference in Junction Split Flow Specifies the convergence tolerance used during the balance of the energy equation. the minimum error solution is checked against the maximum difference in junction split flow tolerance. Flow Tolerance Factor in Weir Split Flow This factor is only used in the bridge and culvert computations. and it is the default selection. If the Automatic Selection option is specified. and then proceeds with the calculations.3-4
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Flow Tolerance Factor This factor is only used in the bridge and culvert computations. this option provides a solution balance. As the software attempts to balance the energy equation. If the solution at minimum error is greater than the maximum difference in junction split flow tolerance. when the computation process cannot find a balance between the assumed and computed water surface elevation. the software selects. The resultant is then used as a flow tolerance for the balance of weir flow and flow through the structure. If the software goes to the maximum number of iterations without meeting the specified calculation tolerance. the solution with the minimum error (assumed minus computed water surface) is saved.
. The computations then proceed from there. issues a warning. The flow tolerance factor is used when the software is attempting to balance between weir flow and flow through the structure. If the solution at minimum error is less than this value. Maximum Number of Iterations in Split Flow Specifies the maximum number of iterations the software makes when attempting to balance the water surface calculations at a split flow location. one of the four computation methods. The flow tolerance factor is used when the software is attempting to balance between weir flow and flow through the structure. Sometimes. This selection is based upon flow conditions. Available friction loss computation methods include: • • • • • Average Conveyance Equation Average of Friction Slope Geometric Mean of Friction Slope Harmonic Mean of Friction Slope Automatic Selection
The Average Conveyance Equation option is recommended for general applications. then the software issues a warning and defaults the solution to critical depth. then the software uses the minimum error solution as the answer. on a step-by-step basis. Friction Loss Computation Method Specifies the computation method to be used in computing friction losses. This factor is multiplied by the total flow.

some minor differences in results can occur in the analysis. If the At Breaks in Roughness Manning’s Only option is selected. This method is the default method. This method should only be used when you feel the software is finding an incorrect answer for critical depth. the software selects the answer with the lowest energy. Increasing the calculation tolerance above the default values could result in computational errors in the water surface profile. The conveyance subareas are then summed to get the total overbank conveyance. approximately 3 times larger in magnitude.Input Descriptions
3-5
Conveyance Computation Method Specifies how conveyance is computed in the overbanks. Always Compute Critical Depth Specifies that critical depth is always computed at every cross section. and therefore different water surface profiles. and conveyance between every coordinate point in the overbanks. but is only capable of finding a single minimum on the energy curve. flow area. the software does not select these answers as valid critical depth solutions unless there is no other answer available. and then calculates the conveyance for this subarea. Since critical depth is calculated often.
Warning
The Calculation Tolerances entries allow you to override the default settings for the calculation tolerances. If more than one minimum is found. When metric units of measure are used.
. These tolerances are used in the solution of the energy equation. If the Between All Ground Points option is selected. This method was the only method available in HEC-2. Adjustments should be made to these tolerances to obtain the desired accuracy in the analysis results. and is regarded as being more accurate. These two methods can provide different answers for conveyance.
Metric Tolerances
If metric (SI) units of measure are used. When this occurs. Critical Depth Computation Method Specifies the method of computing critical depth. these tolerances become meters. The conveyance values are then summed to get the total left overbank and right overbank conveyance. This search method takes a lot of computation time. The Multiple Depth Search method is capable of finding up to three minimums on the energy curve. The Parabolic Search method uses a parabolic searching technique to find the minimum specific energy. Very often the software finds minimum energies at levee breaks and breaks due to specified ineffective flow areas. the software sums the wetted perimeter and the flow area between breaks in roughness n values. using this method slows down computations. Tolerances used in the decision logic of the software are normally in feet. the software calculates the wetted perimeter. This method is very fast.

3. and flow lengths. Note that this ID was assigned when the cross section view was first created.3.3
Cross Section Data
After defining a cross section view and its corresponding ground geometry. roughness. other data describing the cross section can be specified. reach lengths. channel and floodplain roughness.3-6
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
3. Note that cross section IDs must be ascending in value. Up to 5 lines of 72 characters each can be entered. This entry must correspond to one of the entered cross section geometry stations. This data entry must be positive in value and be no more than six characters long. from downstream to upstream. Cross Section ID This data entry is used to specify the ID which uniquely identifies the cross section.
. No two cross sections within the same river reach may have the same cross section ID. To access the Section Description dialog box. In the Section Description dialog box.1).3. This is how BOSS RMS is able to maintain the numerical placement of the current cross section relative to all the other specified cross sections. The software will ensure this by automatically snapping to the closest ground station when picking the overbank station from the cross section plot or topographical map. bank stations. Cross Section Specify the cross section that you want to modify. Description (optional) Specify a description of the current cross section. loss coefficients and other information about the current cross section. Overbank Station: Left Specifies the left floodplain overbank station (looking downstream) that defines the cross section flow region that corresponds to the left floodplain flow length (see Figure 3. The following sections describe how to define other data properties for a cross section. click River tab > Input panel > Section Description.1
Cross Section Description
The Section Description dialog box allows you to specify overbank locations.1. To select the station from the cross section plot or topographical map (if it's visible on-screen) click <. such as contraction and expansion loss coefficients. specify the following parameters: Reach Specify the river reach to which the cross sections belong.

If this entry is left blank. A maximum of 45 flow slices can be defined at a cross section (adding together all of the flow slices defined for the left overbank. such as computing a velocity distribution or for performing bridge scour calculations. such as computing a velocity distribution or for performing bridge scour calculations. channel.Input Descriptions
3-7
Flow Slices: Left Specifies the number of flow slices to construct in the left overbank for computing a flow distribution at the cross section.0 is not permitted. channel. the left floodplain flow length is set equal to the channel flow length. click <. The model uses this distance in computing flow conveyance. and right overbank). The software will allow you to define the flow length by pointing out the flow path on the topographical map. This entry is required for the furthest downstream cross section (when performing a subcritical profile analysis). Manning's n: Left Specifies the Manning's roughness coefficient corresponding to the left floodplain (looking downstream). Flow Slices: Channel Specifies the number of flow slices to construct in the channel for computing a flow distribution at the cross section. A maximum of 45 flow slices can be defined at a cross section (adding together all of the flow slices defined for the left overbank. or for the furthest upstream cross section (when performing a supercritical profile analysis) when horizontal Manning’s roughness busareas are not specified. The computed flow distribution can then be used for determining additional hydraulic properties.
. The computed flow distribution can then be used for determining additional hydraulic properties. This entry must be specified if the cross section locations do not correspond to river stationing. Flow Length: Left Specifies the left floodplain flow length (looking downstream) between the current cross section and the adjacent downstream cross section that the left overbank flow uses. and right overbank). This entry will be ignored for the furthest downstream cross section. If this entry is left blank. then the last value entered for the adjacent downstream cross section (when performing a subcritical profile analysis) or adjacent upstream cross section (when performing a supercritical profile analysis) is used. To automatically measure the distance off of the topographical map (if it's visible on-screen). A Manning's coefficient of 0. Manning's n: Channel Specifies the Manning's roughness coefficient corresponding to the channel.

To select this station from the cross section plot or topographical map (if it's visible on-screen). and right overbank). Manning's n: Right Specifies the Manning's roughness coefficient corresponding to the right floodplain (looking downstream). To automatically measured off of the topographical map (if it's visible onscreen). This entry is required for the furthest downstream cross section (when performing a subcritical profile analysis). then the last value entered for the adjacent downstream cross section (when performing a subcritical profile analysis) or adjacent upstream cross section (when performing a supercritical profile analysis) will be used.
. The software will allow you to define the flow length by pointing out the flow path on the topographical map. or for the furthest upstream cross section (when performing a supercritical profile analysis) when horizontal Manning’s roughness busareas are not specified. Flow Length: Channel This entry specifies the channel flow length between the current cross section and the adjacent downstream cross section. A maximum of 45 flow slices can be defined at a cross section (adding together all of the flow slices defined for the left overbank. The model uses this distance in computing flow conveyance. Flow Slices: Right This entry specifies the number of flow slices to construct in the right overbank for computing a flow distribution at the cross section. The computed flow distribution can then be used for determining additional hydraulic properties. click <. A Manning's coefficient of 0. This entry must be specified if the cross section locations do not correspond to river stationing. Overbank Station: Right Specifies the right floodplain overbank station (looking downstream) that defines the cross section flow region that corresponds to the right floodplain flow length. click <. such as computing a velocity distribution or for performing bridge scour calculations. the channel flow length will be set equal to the computed flow length between the adjacent downstream cross section location and the current cross section location.3-8
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
If this entry is left blank. If this entry is left blank.0 is not permitted. channel. This entry must correspond to one of the entered cross section geometry stations. This entry will be ignored for the furthest downstream cross section. The software ensures this by automatically snapping to the closest ground station when picking the overbank station from the cross section plot or topographical map.

The model uses this distance in computing flow conveyance. generally only one value is used at a particular cross section reach. However. based upon whether it encounters a contracting reach or expanding reach. To automatically measured this distance off of the topographical map (if it's visible on-screen). The software propagates these coefficients from cross section to cross section so they can be defined only once (unless the values change).
. The software automatically uses the appropriate coefficient. or for the furthest upstream cross section (when performing a supercritical profile analysis) when horizontal Manning’s roughness busareas are not specified. The software will allow you to define the flow length by pointing out the flow path on the topographical map. Flow Length: Right Specifies the right floodplain flow length (looking downstream) between the current cross section and the adjacent downstream cross section that the right overbank flow uses. A Manning's coefficient of 0. then the last value entered for the adjacent downstream cross section (when performing a subcritical profile analysis) or adjacent upstream cross section (when performing a supercritical profile analysis) will be used. Both contraction and expansion coefficients are specified at a cross section. This entry will be ignored for the furthest downstream cross section. Contraction Loss Expansion Loss These coefficients are used to compute the contraction and expansion loss components of the energy equation.0 is not permitted. click <. This entry must be specified if the cross section locations do not correspond to river stationing. The default loss coefficients for contraction and expansion is 0. This entry is required for the furthest downstream cross section (when performing a subcritical profile analysis). the right floodplain flow length will be set equal to the channel flow length.Input Descriptions
3-9
If this entry is left blank.0. If this entry is left blank. or the last values entered for the adjacent downstream cross section (when performing a subcritical profile analysis) or adjacent upstream cross section (when performing a supercritical profile analysis).

The floodplain overbank station locations can then be defined from either the cross section view or the topographical map. the software inserts these points into the cross section view’s ground geometry and on the cross section shown in the topographical map (if available). Once the stations and elevations have been entered. Therefore. the overbank station and elevation must be defined in the ground geometry data.0.8
Figure 3.1.3-10
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
The following contraction loss coefficients can be used: No transition loss computed Gradual transition Bridges (or culverts with wingwalls) Abrupt transitions (and most culverts) 0.3. channel modifications.3 0. caution should be exercised when applying the Hydraulic Calculator to these situations.5 0.3 0.1 0.6
The maximum value for the expansion loss coefficient is 1. or levees in which flow has been restricted. This is done manually using the Edit Geometry dialog box.
.1 Flow lengths between cross sections
Channel Overbank Station Locations
If the floodplain overbank station locations to be defined correspond to ground stations that were not entered when the cross section geometry was originally input.0 0.
Hydraulic Calculator
The Hydraulic Calculator considers the entire cross section geometry as available for flow in its computations. conveyance obstructions. The following expansion loss coefficients can be used: No transition loss computed Gradual transition Bridges (or culverts with wingwalls) Abrupt transitions (and most culverts) 0. It knows nothing about ineffective flow areas. floodplain encroachments.0 0.

With this option. An example of this type of ineffective flow area is shown in Figure 3.2. you enter a left station.Input Descriptions
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3. To change an ineffective flow area in the list box. An example of this type of ineffective flow area is shown in Figure 3. select the appropriate entry from the list box. This type of ineffective flow area method is the same as is used in HEC-2.3. To access the Ineffective Flow Areas dialog box.2. The area to the left of the left station and to the right of the right station will be assumed completely ineffective at carrying flow. The software requires that three points be selected when drawing the ineffective flow area. Click Draw to draw the ineffective flow area. specify the following parameters: Type Two alternatives are available for defining ineffective flow areas: • • Normal (HEC-2 Method) Multiple Blocks
Normal (HEC-2 Method) The Normal (HEC-2 Method) type allows you to define a left station and elevation and a right station and elevation.2
Ineffective Flow Area Description
The Ineffective Flow Areas dialog box allows you to restrict flow to the effective flow area of the cross section. and then make the appropriate changes. click River tab > Input panel > Ineffective Flow Areas. Multiple Blocks Multiple Blocks type allows you to define up to 20 individual ineffective flow areas.
. Click Pick to select the left and/or right ineffective flow encroachment station and elevation from the cross section view.1. and an elevation for each ineffective flow area. In the Ineffective Flow Areas dialog box.3.3. a right station.2.

.2 Example of a cross section with multiple ineffective flow areas
Note
Effective flow areas are active only for the current cross section. Therefore. conveyance obstructions. They are not propagated upstream or downstream. or levees in which flow has been restricted.3.3-12
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Figure 3.2.3.
Hydraulic Calculator
The Hydraulic Calculator considers the entire cross section geometry as available for flow in its computations. floodplain encroachments. Therefore. to define the ineffective flow area for a reach of river. channel modifications. It knows nothing about ineffective flow areas. caution should be exercised when applying the Hydraulic Calculator to these situations.1 Example of a cross section with normal ineffective flow areas
Figure 3. more than one cross section must be used to define the ineffective flow region.2.

Blocked obstructions not only decrease flow area. add wetted perimeter when the water comes in contact with the obstruction.3
Conveyance Obstruction Description
The Conveyance Obstructions dialog box allows you to define areas of the cross section that will be permanently blocked out. An example of this type of blocked obstruction is shown in Figure 3. but unlike ineffective flow areas. To access the Conveyance Obstructions dialog box.3.3. a right station. you enter a left station. and an elevation for each blocked obstruction.Input Descriptions
3-13
3. An example of this type of blocked obstruction is shown in Figure 3.3.3.1. Click Pick to select the left and/or right blocked obstruction station and elevation from the cross section view. click River tab > Input panel > Conveyance Obstructions.3.2.1 Example of a cross section with normal blocked obstructions
.
Figure 3. Type Two alternatives are available for defining conveyance obstructions: • • Normal Multiple Blocks
Normal The Normal type allows you to define a left station and elevation and a right station and elevation. Multiple Blocks The Multiple Blocks type allows you to define up to 20 individual blocked obstructions.3. In the Conveyance Obstructions dialog box. The area to the left of the left station and to the right of the right station will be completely blocked out. A blocked obstruction does not prevent water from going outside of the obstruction. specify the following parameters.3. With this option.

It knows nothing about ineffective flow areas. enter the following parameters: Left Levee Station Left Levee Elevation When the water surface elevation is less than the left levee elevation. floodplain encroachments.3-14
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Figure 3. Levee stations must be defined explicitly or the software assumes that water can go anywhere within the cross section.3.3.
3. Therefore. Therefore. click River tab > Input panel > Levees. In the Levees dialog box. or levees. To access the Levees dialog box.
Hydraulic Calculator
The Hydraulic Calculator considers the entire cross section geometry as available for flow in its computations. Click Pick to select the left levee station and elevation from the cross section view.4.3. caution should be exercised when applying the Hydraulic Calculator to these situations. channel modifications. They are not propagated upstream or downstream. to define a blocked obstruction for a reach of river. no water can go to the left of the left levee station or to the right of the right levee station until either of the levee elevations are exceeded. When levees are established. more than once cross section must be used to define the blocked obstruction.2 Example of a cross section with multiple blocked obstructions
Note
Blocked obstructions are active only for the current cross section. conveyance obstructions.
.3.4
Levee Description
The Levees dialog box allows you to define a left and/or right levee station and elevation for the cross section.1). water is not allowed to exceed the specified left levee station (see Figure 3.

Therefore. which specifies whether flow should be contained between the channel banks until the banks are overtopped. when a HEC-2 model that contains X3-IEARA data is imported into HEC-RAS.4. Additional wetted perimeter is included when the water comes into contact with the levee wall. A simple way to do this is to set a levee station and elevation that is above the existing ground. the software warns of this potential problem to the end user in the HEC-2 import log file it generates. Therefore.3. Right Levee Station Right Levee Elevation When the water surface elevation is less than the right levee elevation. the model water surface profile results can differ greatly. to maintain consistency between HEC-RAS’ import behavior.4. Autodesk River Analysis also ignores the X3-IEARA data field when importing the data into HEC-RAS.1). Selecting the Use Right Bank option automatically causes HEC-RAS to maintain the flow within the right bank until the right bank becomes overtopped.1 Example of the levee option
Note
The user may want to define levees in a model to see what effect a levee will have on the water surface elevation.
Figure 3.Input Descriptions
3-15
Selecting the Use Left Bank option automatically causes HEC-RAS to maintain the flow within the left bank until the left bank becomes overtopped. If a levee elevation is placed above the existing geometry of the cross section.
. then a vertical wall is placed at that station up to the established levee height. water is not allowed to exceed the specified right levee station (see Figure 3.
Problems with Imported HEC-2 Data
The standard US Army Corps of Engineers HEC-RAS software does not account for the HEC-2 X3-IEARA data field.3. Click Pick to select the right levee station and elevation from the cross section view. However.

Hydraulic Calculator
The Hydraulic Calculator considers the entire cross section geometry as available for flow in its computations.5
Profile Adjustments Description
The Profile Adjustments dialog box allows you. Cross Section Specify the cross section to which the profiles belong. water surface elevation increment.3-16
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
To maintain the same characteristics for HEC-RAS as with HEC-2. the Flow Discharge dialog box is used to account for the loss of flow upstream of the confluence junction. caution should be exercised when applying the Hydraulic Calculator to these situations. Discharge Specify a known discharge for each profile. Note that this dialog box is generally left blank. energy change. or levees. floodplain encroachments. Reach Specify the reach to which the cross sections and profiles belong. Adjustment Type Specifies the adjustment type for each profile: • • • • • Known water surface elevation Change in water surface Change in energy grade Additional energy grade K loss
If a water surface is known to occur for a particular profile at this cross section. Therefore.3. or additional energy losses for the current cross section. as occurs in a tributary stream network. conveyance obstructions. This entry is used to account for change in discharge due to river inflow and outflow. In the Profile Adjustments dialog box. select the Use Left Bank and Use Right Bank options at those cross sections that Autodesk River Analysis warns the user of. To access the Profile Adjustments dialog box. a different discharge and an optional known water surface elevation. click River tab > Input panel > Profile Adjustments. It knows nothing about ineffective flow areas. enter the following parameters. channel modifications.
. then specifying Known WS will allow you to specify this elevation.
3. However. on a profile basis. when a lateral inflow occurs along the stream being modeled.

6
Rating Curve Description
The Rating Curve dialog box allows you to specify a discharge versus elevation rating curve for the current cross section. click River tab > Input panel > Rating Curve. enter a new value in the data entry. Discharge Specifies the corresponding measured discharge. In the Rating Curve dialog box. The software will then use this to compute a water surface elevation from the specified change in energy. Selecting Additional EG allows you to enter an additional energy loss between the adjacent downstream cross section and the current cross section for a particular profile. These values will then be used in the analysis. instead of being computed. If a specific energy change is to occur between the adjacent downstream cross section and the current cross section in order to obtain the energy gradeline elevation at the current cross section for a particular profile.
Caution
The Profile Adjustments dialog box should not be used to define profile adjustments for either the most downstream or most upstream cross section.3. select the appropriate profile entry from the list box.
Changing Entries
To add or change any values in the list box.Input Descriptions
3-17
If a water surface elevation increment is to be added to the water surface elevation of the adjacent downstream cross section to obtain the water surface elevation at this cross section for a particular profile.
Linkage with Specified Profiles
The list box values specified in the Profile Adjustments dialog box correspond to specific starting conditions defined for profiles contained in the Profile Description dialog box. then specifying Change in WS allows you to specify this elevation increment. specify the following parameters: Note that this dialog box is generally left blank. To access the Rating Curve dialog box. then specifying Change in EG allows you to specify this change in energy. This is generally done when accurate field observations have been collected. and choose Apply. This energy loss gets added to the computed energy losses that occur during the balancing of the energy equation.
3.
. The software updates the value contained in the list box. A maximum of 100 rating curve values can be specified.

Water Surface Elevation Specifies the water surface elevation for which a known discharge has been measured. To add a rating curve point to the list, select an empty entry from the list, and then enter the point's discharge and water surface elevation values. The software automatically inserts the rating curve point into the list in sorted order according to water surface elevation.

Note
The software linearly interpolates between given rating curve values and extrapolates for values outside the specified rating curve range. If accurate discharge versus elevation data is not known for the cross section, then these data entries should be left blank.

3.3.7

Horizontal Roughness Description
The software's Edit Geometry dialog box allows you to specify horizontal roughness subareas for the current cross section view's ground geometry. To access the Edit Geometry dialog box, click River tab > Input panel > Horizontal Roughness. The Section Geometry Editor dialog box allows you to define horizontal Manning's n roughness coefficients for subareas of the current cross section. A Manning's coefficient of 0.0 is not permitted. When specified, these coefficients replace any Manning's n coefficients specified in the Cross Section Description dialog box. These horizontal subarea roughness coefficients need to be specified only when the generalized Manning's roughness coefficients (i.e., left overbank, channel, and right overbank) cannot adequately define the cross section roughness. Horizontal subarea roughness coefficients should not be specified if channel modifications have been specified for the cross section. Roughness coefficients remain in effect until changed at a subsequent cross section. They should be redefined for each cross section that has different ground geometry stationing defined. Roughness coefficients are entered such that they define the subarea to the left (looking downstream) of the corresponding horizontal station (see Figure 3.3.7.1). Each roughness subarea must end at a previously defined ground geometry point. To add a new roughness subarea, specify the ending (rightmost) ground station either by entering the station directly into the data entry, or select the ground station from the cross section view or topographical map by clicking Pick from the Horizontal Station and Ground Elevation data entries. After selecting an ending station, enter the corresponding Manning's n roughness coefficient in the data entry. Double-clicking on a row of data shown in the list box immediately moves the data entry cursor to the ground elevation data entry, thereby allowing you to quickly alter the elevation for an existing ground station.

Input Descriptions

3-19

To delete a row of data from the list box, select the data row from the list. Right-click the row, and click Delete Row(s).

Figure 3.3.7.1 Manning’s roughness coefficient subareas

3.4

Defining Bridge and Culvert Openings
When defining bridge or culvert flow structures, the flow structure must be declared at the cross section corresponding to the downstream face of the structure. The flow structure is declared using the Bridge & Culvert Openings dialog box. To access the Bridge & Culvert Openings dialog box, click River tab > Input panel > Bridges & Culverts drop-down > Bridge & Culvert Openings. The Bridge & Culvert Openings dialog box defines all of the components that make up the selected flow structure. After selecting the appropriate Cross Section Type, additional buttons become available to define the type of flow structure and its components. In the Bridge & Culvert Openings dialog box, specify the following parameters: Cross Section Type Define the downstream face as a Bridge or Culvert. If a flow structure is not declared at this cross section, then this entry must be set to No Opening. If a Bridge or Culvert structure is specified as the current Cross Section Type, specifying No Opening causes the software to not include the flow structure in the analysis. This allows you to quickly alter a model, without having to change or delete the data used to define the structure. For example, you could remove a flow structure to analyze the unconstricted natural water surface profile at a location. Or, you might want to perform a water surface profile comparative analysis between a bridge and a culvert at the same location.

The bridge and/or culvert structure is declared only at the cross section that corresponds to the downstream face of the structure. For all other related bridge and/or culvert cross sections, this data entry must be set to No Opening. If specifying a bridge flow structure, then this must be set to Bridge at the cross section corresponding to the downstream face of the bridge structure. Selecting this entry will make additional data entry buttons available, allowing the bridge flow structure components to be defined. All other cross sections at this bridge structure must be set to No Opening. If specifying a culvert flow structure or a group of culverts, then this must be set to Culvert at the cross section corresponding to the downstream face of the culvert structure. Selecting this entry will make additional data entry buttons available, allowing the culvert flow structure components to be defined. All other cross sections at this culvert structure must be set to No Opening.

Maximum Number of Flow Structures
A maximum number of 7 flow structures, of any combination (i.e., bridge, culvert, and/ or conveyance flow area), can be defined at a cross section. However, within a culvert flow structure (also called a culvert group—which counts as a single flow structure), up to 25 culvert barrels can be defined.

Stagnation Points
Stagnation points are the locations at which flow separates (on the upstream side) from one opening to the next adjacent opening.
.

Figure 3.4.1 Multiple opening cross section

The cross section ground geometry starting and ending stations must correspond with that of the starting flow structure’s leftmost station and the ending flow structure’s rightmost station. Also, there cannot be any gap in stationing between flow structures, and in fact stationing between bridges and/or culverts can be allowed to overlap. As shown in the previous image, the right station of the culvert group overlaps with the left station of the bridge opening. When overlapping stationing is defined, HEC-RAS automatically calculates the location of the stagnation point within the defined stationing overlap. This allows the stagnation point to vary from one profile to the next.

Under either Downstream XS or Upstream XS. select Bridge. 2.
3. The software will display the applicable cross section view and the Section Geometry Editor dialog box.
3. To define the bridge low chord geometry. an error message describes the problem. 4.1
Direct Editing Input Method
The direct edit method displays the Edit Geometry dialog box. To access the Bridge & Culvert Openings dialog box. Select the downstream face cross section for the defined bridge.
3. The low chord geometry and roadway geometry of a bridge are used to define the bridge flow characteristics. and delete individual low chord and roadway geometry points of a bridge. 5. On the Bridge & Culvert Openings dialog box. If you try to define the bridge low chord geometry and no ground geometry exists at the cross section. On the Bridge & Culvert Openings dialog box. These input methods include the following: • • • Entering and editing low chord geometry coordinate points directly in a dialog box Drawing the low chord geometry directly on the screen Digitizing the low chord geometry from a paper cross section plot
The following sections describe these methods for defining the bridge low chord geometry. This data must be specified at both the downstream and upstream face bridge cross sections. click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. first specify an existing ground station either by entering the station value directly into the data entry. select Bridge. The Bridge & Culvert Openings dialog box allows you to select an input method for defining the bridge low chord geometry. To add a new low chord and/or roadway geometry point. or by clicking Pick to select the ground station from the cross section view or topographical map.
. edit. To enter low chord data directly: 1.5
Defining the Bridge Low Chord Geometry
The bridge flow structure is specified using the Bridge & Culvert Openings dialog box.Input Descriptions
3-21
However. click Edit Geometry. the interior stationing for a conveyance flow area must be defined to match the adjacent flow structure’s stationing—no overlap is allowed.5. click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. existing ground geometry must already exist at the cross section. which can be used to insert.

3. For more precision.3-22
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
6.
7. the low chord station value will be updated to match the nearest ground station.
9. To delete a row of data from the list box.2
Screen Cross Section Input Method
The screen cross section input method allows you to define new low chord geometry on-screen for the currently active cross section view. select the point from the list box or click Pick to select it from the cross section view.
3.3
Graphical Adjustment of Low Chord Geometry
You can perform bridge low chord geometry adjustments graphically using grips.1320. and then pan to move about.
After selecting a ground station.
8.
3.5. 2.5. 4. select Bridge. the software makes certain that each low chord station matches an existing ground station. Select the downstream face cross section for the defined bridge.
. allowing you to enter new low chord geometry points by clicking anywhere on the grid or by typing in station and elevation coordinates (such as 100. Under either Downstream XS or Upstream XS. select the data row from the list and click Delete. To enter low chord geometry on screen: 1. On the Bridge & Culvert Openings dialog box. Double-clicking on a row of data shown in the list box will immediately move the data entry cursor to the ground elevation data entry. If not. The software displays the applicable cross section view. Click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. Then modify the elevation value in the appropriate data entry. Pick the point you want to move and drag it to its new location. Pick the line representing the bridge low chord with the cursor to move an individual low chord geometry point shown on the cross section view. you will have greater precision in defining the low chord geometry. As you define the bridge low chord geometry using this method. you may wish to zoom in. with no spaces). To edit an existing low chord and/or roadway geometry point. or click Pick to select the elevation from the cross section view. thereby allowing you to quickly alter the elevation for an existing ground station. click Draw Low Chord. enter the low chord and/or roadway elevation into the appropriate data entry.

while the span represents the maximum inside width. The culvert parameters and roadway geometry define the culvert flow characteristics. The rise refers to the maximum inside height of the culvert. This is because HEC-RAS computes the conveyance for a bridge opening using a series of trapezoids whose vertical sides correspond to the defined low chord and ground geometry stationing. Both circular and semi-circular culverts are defined by entering a diameter.
Shape Specifies a culvert shape. To define culverts: 1. including: • • • • • • • • • Circular Box (or rectangular) Pipe Arch Pipe arch Ellipse Semi-Circle Low arch High arch Conspan Arch
The size of the culvert is defined by entering a rise and span. Select the downstream face cross section for the culvert.
3. Autodesk River Analysis. In the Define Culverts dialog box. a warning message is displayed. 2. select Culvert.
. 4. The roadway geometry must be specified at both the upstream and downstream face culvert cross sections. If not. click Define.Input Descriptions
3-23
Low Chord Geometry Station Alignment
It is important to make certain that a moved low chord geometry station matches an existing ground point station. On the Bridge & Culvert Openings dialog box.6
Defining Culverts
A single or group of culvert flow structures is declared using the Bridge & Culvert Openings dialog box. Click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. specify the following parameters:
3. when it generates the data transfer file. automatically checks that the bridge low chord stationing corresponds to the specified cross section ground stationing. Under either Downstream XS or Upstream XS. 5.

size.. Outlet control flow occurs when the culvert flow capacity is limited by downstream conditions (e. each with a different centerline station. To copy a specified centerline station. It is common to use the concept of inlet control and outlet control to simplify the analysis. The analysis of flow in culverts is quite complicated.6. By selecting the Highest Upstream Energy Elevation. select the appropriate entry from the Culvert Details list and click Copy. However.Input Descriptions
3-31
Figure 3.g. Centerline Stationing Defines multiple culverts. Multiple culverts defined this way are called a culvert group. To delete a culvert. Inlet control flow occurs when the flow capacity of the culvert entrance is less than the flow capacity of the culvert barrel. The water surface passes through critical depth at or near this location and the flow regime immediately downstream is supercritical.
. The control section of a culvert operating under inlet control is located just inside of the culvert entrance. To change a culvert stationing entry. HEC-RAS computes the upstream energy required to produce a given flow rate through the culvert for both inlet and outlet control conditions. and loss coefficients. It is recommended that the default Highest Upstream Energy Elevation be selected. high tailwater) or by the flow carrying capacity of the culvert barrel. the higher upstream energy gradeline elevation controls and thereby determines the type of culvert flow for a given flow rate and tailwater condition. and then enter the new values. To add a new culvert to the Culvert Details list. these culverts must have identical shape. select the appropriate entry from the Culvert Details list and click Delete. invert elevations. select the appropriate entry from the Culvert Details list. Each culvert can have a different downstream and upstream station value. enter the corresponding downstream and upstream centerline stations into the data entries and click Add.12 Offset flared wingwalls (FHWA Chart 13)
Solution Criteria Specifies which culvert solution to use when computing the flow through a culvert.

This slope is then used to compute the normal depth of flow in the culvert under inlet control conditions. you should reduce the box culvert opening width. but also in determining whether the headwater and tailwater elevations are adequate to submerge the inlet or outlet of the culvert. Click Pick to graphically measure the culvert opening width.6. A sufficient slope to maintain a minimum flow velocity of three feet per second (or one meter per second) is often required. If you wish to consider the loss in area due to the chamfers. The software uses this value to compute the culvert slope. HEC-RAS cannot analyze culverts with adverse (negative) slopes. The culvert length is used to determine the friction loss in the culvert barrel and the slope of the culvert. enter the width of only a single box culvert. considering the reduction in area caused by the chamfered corners.6. Culvert Downstream Invert Specifies the culvert opening downstream invert elevation (see Figure 3. Some manufacturers' literature contains the true cross sectional area of each size box culvert. Culvert Length Specifies the culvert length. The inside height (or diameter) of the culvert opening is important not only in determining the total flow area of the culvert. not the accumulated width of all the culverts.2). If analyzing a pipe culvert. because the software uses the culvert height to determine the submergence of the culvert inlet and outlet. leave this entry blank.6.1 and Figure 3. even under low flow conditions. Therefore. the downstream invert elevation must be equal to or less than the upstream invert elevation so that some flow velocity can be maintained in the culvert. Width or Span Specifies the inside width of the box culvert. Click Pick to graphically measure the culvert diameter or height.
. You should not reduce the box culvert height.6. These chamfers are ignored by HEC-RAS in computing the cross sectional area of the culvert opening. Most box culverts have chamfered corners on the inside. Distance to Upstream XS Specify the distance to the cross section immediately upstream. The culvert length is measured along the centerline of the culvert.2). Click Pick to graphically select the culvert opening downstream invert elevation from the cross section view.1 and Figure 3. If multiple box culverts exist.3-32
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Diameter or Height Specify the inside diameter of a pipe culvert or the inside height of a box culvert (see Figure 3. Click Pick to graphically measure the distance.

Therefore.2). This slope is then used to compute the normal depth of flow in the culvert under inlet control conditions. The software uses this value to compute the culvert slope. HEC-RAS cannot analyze culverts with adverse (negative) slopes. or greater than. Downstream Invert Specifies the culvert opening downstream invert elevation (see Figure 3.1 and Figure 3.5 list some suggested values for culvert entrance loss coefficients. even under low flow conditions. Entrance Loss Coefficient Specifies the culvert entrance loss coefficient to be used in computing the head loss at the culvert entrance. A sufficient slope to maintain a minimum flow velocity of three feet per second (or one meter per second) is often required. This slope is then used to compute the normal depth of flow in the culvert under inlet control conditions. Table 3. The software uses this value to compute the culvert slope. HEC-RAS cannot analyze culverts with adverse (negative) slopes.2).Input Descriptions
3-33
Click Pick to graphically measure the length of the culvert. This value represents the amount of energy loss that occurs as flow enters the culvert. even under low flow conditions.6. The coefficient entered in this data entry will be multiplied by the change in velocity head inside the culvert at the upstream end. the upstream invert elevation must be equal to.6.
. Click Pick to graphically select the culvert opening downstream invert elevation from the cross section view.4 and Table 3.6. Upstream Invert Specifies the culvert opening upstream invert elevation (see Figure 3. Therefore.6. the upstream invert elevation so that some flow velocity can be maintained in the culvert. the downstream invert elevation must be equal to. A sufficient slope to maintain a minimum flow velocity of three feet per second (or one meter per second) is often required. or greater than. the upstream invert elevation so that some flow velocity can be maintained in the culvert. Click Pick to graphically select the culvert opening upstream invert elevation from the cross section view.6.1 and Figure 3.6.

7..
3.e. Selecting WSPRO Method and then clicking Define will display the WSPRO Bridge Parameters dialog box (see the following section titled WSPRO Bridge Parameters).] to display a table that lists the typical drag coefficients for various pier shapes. By default. The Bridge Computation Methodology dialog box is displayed when you click Methodology on the Bridge & Culvert Openings dialog box when defining a bridge flow structure. since this represents typical roadway overflow situations. Pier Shape Coefficient If the Yarnell computation method is to be used in computing Class A low flows. If this entry is left blank and a pier geometry is specified. Select any of the appropriate Compute options to enable HEC-RAS to compute any or all of the low flow answers.7
Other Bridge Data
The following sections describe additional data used to define a bridge.. Pier Drag Coefficient If the Momentum computation method is to be used in computing Class A low flows. Click [.
. which allows you to define data for the WSPRO bridge computational method. the Highest Energy Answer is used and only the Energy computation method is used.1
Bridge Computation Methodology
The Bridge Computation Methodology dialog box allows you to specify the computation method to be used in computing Class A low flow conditions and high flow conditions (flow at or above the maximum low chord elevation). High Flow Computation Method Instructs the software to use a particular high flow computation method when computing high flow conditions (i. By default the Pressure and Weir computation method is selected. Class A Low Flow Computation Method (optional) Instructs the software to use a particular low flow computation method answer when computing Class A low flow conditions. The Energy computation method selection uses only the energy based method (in the same manner as is computed for low flows) to compute the high flows— and is generally only used in severe roadway overtopping situations where weir flow is submerged. when the bridge low chord is submerged).. Click [.Input Descriptions
3-37
3.. then you must specify the pier shape coefficient.] to display a table that lists the typical drag coefficients for various pier shapes. then you must specify the drag coefficient to be used in calculating pier losses in the momentum equations. then the software will use the drag coefficient associated with square piers..

Click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. On the Bridge and Culvert Openings dialog box. When both the upstream and downstream sides of the bridge are submerged. To access the WSPRO Bridge Parameters dialog box: 1. This discharge coefficient can range from 0.
3.9.2
WSPRO Bridge Parameters
The WSPRO Bridge Parameters dialog box allows you to define data for the WSPRO bridge computational method.7.7 to 0. This data entry thereby allows you to specify a higher (or lower) trigger elevation to be used (in place of the maximum low chord elevation) to initiate the pressure flow water surface elevation calculation.35 to 0. In the WSPRO Bridge Parameters dialog box. You can enter a fixed value for this coefficient or the software will compute one based on the amount that the inlet is submerged. enter the following parameters:
2.
. Click Define. This discharge coefficient is not used in the energy based computation method. with a value of 0.3-38
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
The Pressure and Weir computation method selection uses separate hydraulic equations to compute the flow as pressure and/or weir flow. This discharge coefficient is not used in the energy based computation method.
4. the pressure flow water surface elevation is compared to the low flow water surface elevation and the higher of the two elevations is assumed to control. On the Bridge Computation Methodology dialog box. You can enter a fixed value for this coefficient or the software will compute one based on the amount that the inlet is submerged. Pressure Flow Trigger Elevation (optional) Overrides the maximum low chord elevation to be used by the software when checking for the possibility of pressure flow. This discharge coefficient can vary depending upon the depth of water upstream.5 commonly used in practice.5. Click Methodology. The software checks for the possibility of pressure flow when the computed low flow energy gradeline elevation is above the maximum low chord elevation at the upstream side of the bridge. Values can range from 0. select Bridge.8 commonly used in practice. then the pressure flow water surface elevation is computed. the standard full flowing orifice equation is used. with a value of 0. Next. If this energy gradeline elevation is above the maximum low chord elevation.
3. Submerged Inlet Discharge Coefficient (optional) Specifies the coefficient of discharge for submerged inlet pressure flow. Submerged Inlet and Outlet Discharge Coefficient (optional) Specifies the coefficient of discharge for both submerged inlet and outlet pressure flow. select WSPRO Method.

then this field is not available. the software automatically centers the computed top width. If the left and right bridge abutments do not have the same slope. which is an integral part in the calculation of the WSPRO bridge discharge coefficient. If the bridge abutments are vertical. Click Pick to define the embankment toe elevation by selecting it from the cross section view. There are four abutment types available: • • • • Vertical abutments and embankments with or without wing walls Vertical abutments and sloping embankments Sloping abutments and sloping embankments Vertical abutments and sloping embankments with wing walls
Abutment Slope Specifies the bridge abutment slope. use the average of the two widths. This slope is taken as the horizontal distance divided by the vertical distance. This conveyance is used in calculating a channel contraction ratio. Left Embankment Toe Elevation Right Embankment Toe Elevation Specify the abutment toe (elevation at the station in which the abutment toe intersections with the natural ground inside of the bridge opening) elevation on both the left and right side of the bridge opening.
. it is necessary to calculate the water surface top width inside of the bridge opening. This list affects the availablility of some of the wing wall data entries that are contained in this section. Click Pick to define the embankment top elevation by selecting it from the cross section view. Click Pick to define the centroid station graphically. If the top width of the embankment varies from one end of the bridge opening to the other. top of road) elevation at the edges of the bridge opening. Embankment Top Width Specifies the top of the road embankment width. You can override this by entering a known centroid stationing value for the approach cross section. such that the center of the top width will be at the center of conveyance at the approach cross section..e. Left Embankment Top Elevation Right Embankment Top Elevation Specify the top of the embankment (i. Click Pick to measure the embankment top width from the surface.Input Descriptions
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Abutment Type Specifies the bridge abutment type. HEC-RAS computes the conveyance within this projected width at the approach cross section. An elevation must be entered for both the left and right side of the bridge opening. in the area of the bridge opening. Centroid Stationing of Projected Bridge Opening at the Approach Cross Section For the WSPRO computational method. If this field is left blank. Wing Wall Type Specifies the type of wing walls present at the bridge opening. and then project that width onto the approach cross section. use the average of the two slopes.

measured relative to the flow direction. Click to measure the wing wall length from the surface. Wing Wall Length Specifies the length of the wing wall. Do not specify these additional losses unless you believe that the standard WSPRO bridge method is not producing enough energy loss through the bridge. To access the WSPRO Bridge Parameters dialog box:
. Optional Contraction and Expansion Losses These options allow you to specify additional contraction and expansion losses to be computed at locations that are not traditionally in the standard WSPRO bridge methodology. measured relative to the bridge opening. Guide Bank Type Specifies the type of guide bank present at the bridge opening. This is selected by default. if the wing wall entrance is rounded. This is selected by default.7. Guide Bank Offset Specifies the offset of the guide bank. Guide Bank Length Specifies the length of the guide bank. Guide Bank Skew Angle Specifies the skew angle of the guide bank. Click Pick to measure the guide bank offset from the cross section view. Note that these parameters apply for all bridges defined within the model. The standard WSPRO bridge method only computes expansion losses in the expansion reach (between the bridge downstream face cross section and the exit cross section). Click Pick to measure the wing wall entrance rounding radius from the surface. Click Pick to measure the guide bank length from the surface.3
Global Bridge Parameters
The Bridge Parameters dialog box allows you to specify additional parameters to be used when computing flow through a bridge. Entrance Rounding Radius Specifies the entrance rounding radius. measured starting from the bridge abutment.3-40
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Wing Wall Angle Specifies the angle of the wing wall. This list affects the availablility of some of the guide bank data entries that are contained in this section. measured starting from the bridge abutment. measured relative to the flow direction. Use Geometric Mean as Friction Slope Method Specifies whether to use the Geometric Mean as the friction slope method. Piers are Continuous for the Width of Bridge Specifies whether the piers are continuous for the whole way through the bridge.
3.

By default. Then. By default. However. If this energy gradeline elevation is above the maximum low chord elevation.4
Bridge Pier Description
The Define Piers dialog box allows you to specify centerline locations and dimensions for each individual bridge pier. If the piers are included with ground or low chord geometry. Pressure Flow Criteria Specifies the overridden cross section when pressure flow calculations are to be initiated. The mixed flow regime mode is capable of calculating a subcritical profile upstream of the bridge and a supercritical profile downstream from the bridge. Since the weight component does not generally add much in terms of additional momentum losses. On the Bridge and Culvert Openings dialog box. Also. The HEC-RAS low flow bridge computations require that the piers be defined separately in order to determine the amount of area under the water surface that is blocked by piers.
Click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. you should run the model in a mixed flow regime mode. the pressure flow water surface elevation is computed. if they exist.7. This option is specified in the Profile Description dialog box. Critical Depth Location Specifies the overridden cross section the critical depth is to be computed for determining whether Class B low flow exists.
3. it is not selected by default. To access the Define Piers dialog box:
.Input Descriptions
3-41
1. the software checks for the possibility of pressure flow when the computed low flow energy gradeline elevation is above the maximum low chord elevation at the upstream side of the bridge. several of HEC-RAS’ low flow computational methods will incorrectly compute the amount of energy loss.
2. select Bridge. this data entry allows you to specify that the computed water surface elevation should be used in place of the computed energy gradeline elevation for determining when pressure flow calculations are to be initiated. the pressure flow water surface elevation is compared to the low flow water surface elevation and the higher of the two elevations is assumed to control.
Momentum Equation (optional) Specify additional loss components to add to the momentum equation when computing Class A low flow. However. Click Parameters.
Note
Whenever Class B low flow is found to exist in a model. any hydraulic jumps will be located. the critical depth will be computed at the upstream end of the bridge opening. the friction component is selected by default.

Pier Geometry Considerations
Pier geometry is entered as pier elevation and width valued pairs. this data is optional. Any pier area below the ground elevation or above the low chord elevation (but less than the roadway elevation) is clipped off automatically. Click Sloping Abutments. To access the Define Abutments dialog box: 1. or pier cap) are entered by specifying two widths at the same elevation. If the pier width is to vary uniformly over the elevation range between two pier elevation-width entries. On the Bridge and Culvert Openings dialog box. Generally. Click Piers. pier elevations start below the ground level.3-42
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1. HEC-RAS linearly interpolates the width of the pier between the two elevations.
2. the elevation-width pairs listed in the Pier Obstruction Dimensions table will change. that define the elevation and corresponding width for both the downstream and upstream ends of the pier. such as at a pier footing.
3.
Pier Centerline Stationing Defines the downstream and upstream centerline station locations for each bridge pier. and is only necessary when the cross section channel geometry does not adequately define the bridge opening geometry. defined in the Pier Obstruction Dimensions table.
2.
.7. The geometry of the bridge pier is entered as elevation and width paired values for both the downstream and upstream ends of the pier. However. Each pier has associated with it dimensions.g. Pier widths that change at a single elevation (e. Click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. a left and right abutment are entered for each bridge opening at both the bridge downstream and upstream cross sections. Pier Obstruction Dimensions Defines the geometry for a single bridge pier. The geometry values will automatically be placed in the pier geometry table. Generally. Scrolling through the listed piers. pier armored protection.
Click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. This allows you to further restrict the channel geometry to accurately represent the available bridge opening flow area.5
Bridge Abutment Description
The Define Abutments dialog box allows you to specify bridge abutment geometry whenever bridge abutments protrude out from the defined ground geometry.. select Bridge. sorted based upon elevation. select Bridge. On the Bridge and Culvert Openings dialog box.

Scrolling through the listed abutments. click Draw. the geometry values listed in the above Abutment Geometry table will change.
Abutment Geometry Considerations
Abutment geometry is entered as station and elevation valued pairs. click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. Drawing the abutment geometry deletes all previously defined geometry for the current abutment.
.
3. Select the downstream face cross section for the defined bridge. edit. Abutment Geometry Defines the station and elevation geometry values for a single abutment.Input Descriptions
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Abutment Definition Defines the abutments for the current cross section. To draw the abutment geometry on the cross section view. To define roadway geometry. an abutment must be added to this list.8
Defining the Roadway Geometry
The roadway geometry at a bridge or culvert structure is used to define the structure's road overflow characteristics. At least two points must be specified to describe an abutment. The Opening Definitions dialog box allows you to select an input method for defining the roadway geometry. and delete individual roadway geometry points for a bridge or culvert. The area below the abutment station and elevation is filled in and considered part of the ground.8. These input methods include the following: • • Entering and editing roadway geometry coordinate points directly in a dialog box Drawing the roadway geometry directly on the screen
The following subsections describe these methods for defining the roadway geometry. In general.1
Inputting Roadway Geometry Directly
The Edit Geometry dialog box can be used to insert. Before a bridge abutment geometry can be defined. To enter roadway geometry data directly: 1. it is usually only necessary to enter two points to describe each abutment. sorted based upon station. This data must be specified at the bridge and culvert downstream and upstream cross sections. The geometry values are automatically placed in the abutment geometry table.
3.

However. or by entering it graphically by clicking <.
Click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings. 4.8.5 for a broad-crested rectangular shaped weir to 3. Under either Downstream XS or Upstream XS. In the Section Geometry Editor dialog box.
3.8. To display the Roadway Overflow dialog box. allowing you to enter new roadway geometry points either by clicking anywhere on the grid or by typing in station and elevation coordinates (such as 100. click Draw Road. Select the downstream face cross section for the defined bridge.
3. 2. On the Bridge & Culvert Openings dialog box. On the Bridge & Culvert Openings dialog box. Typical values range from 2. 5. To enter roadway geometry data graphically: 1. generally a value of between 2. Under either Downstream XS or Upstream XS.
3.6 should be used for typical roadway crossings.2
Inputting Roadway Geometry Graphically
The screen roadway input method allows you to define new roadway geometry onscreen for the currently active cross section view.
. select Bridge. You can specify an existing ground station or elevation either by entering the station value directly into the data field. 4. add a new roadway geometry point.1320.3-44
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
2.
3. with no spaces). click River tab > Input panel > Bridges and Culverts drop-down > Roadway Overflow. Weir Flow Coefficient Specifies the coefficient of discharge for use in the weir flow equation. select Bridge.5 and 2. River Analysis displays the applicable cross section view. click Edit Geometry. in the Deck/Roadway Data section.0 for a trapezoidal shaped weir.9
Roadway Overflow Parameters
The Roadway Overflow dialog box allows you to define the roadway overflow characteristics for modeling weir flow at a roadway crossing so that HEC-RAS can accurately model the weir flow.3
Graphical Adjustment of Roadway Geometry
Autodesk River Analysis allows you to perform roadway geometry adjustments graphically using AutoCAD grips. Click River tab > Input panel > Bridges & Culverts > Bridge & Culvert Openings.
3.

Click Pick to graphically measure this distance from the plan view. Roadway Width Specifies the width of the bridge roadway (measured along the flow direction). the software automatically switches to energy based (standard step method) flow calculations. This entry is only used for the FHWA WSPRO bridge method for low flow. However. Road Elevation Defines the minimum elevation at which weir flow begins. HEC-RAS scans through the specified roadway geometry to determine the minimum roadway elevation. rather than standard pressure and weir flow calculations. Upstream Embankment Slope Specifies the embankment side slope of the bridge abutment (measured in the direction of flow) on the upstream face of the bridge. This entry represents the number of horizontal units per one vertical unit for the abutment side slope. If this data entry is left blank. At the cross sections inside the bridge (internally manufactured by HEC-RAS). you can use this entry to artificially raise or lower the minimum elevation at which weir flow is considered. Bridge Rail to Section Distance Specifies the distance from the upstream side of the bridge deck (upstream bridge rail) to the cross section immediately upstream of the bridge (bridge upstream face cross section). Normally this value is 0. the area obstructed by the bridge piers and bridge deck is subtracted from the flow area and additional wetted perimeter is added. Leaving this entry blank causes the software to default to an abutment with vertical side slopes.0 unless the bridge deck is indented from the upstream face cross section. If this ratio is exceeded. The energy based method performs all flow computations as though they are for open channel flow. a default maximum submergence ratio of 0. Click Pick to graphically measure this distance from the plan view.Input Descriptions
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Maximum Submergence Ratio Specifies the maximum allowable submergence ratio that can occur during weir flow over the bridge deck. If this entry is left blank. Click Pick to graphically select the roadway crest elevation from the cross section view. Energy losses are based on friction losses and contraction and expansion losses.95 (95%) is used. in the computation of the bridge discharge coefficient.
.

1965). If any observed data is available. in the computation of the bridge discharge coefficient. but these are the only cross sections that will be used in the bridge scour
. In general. The next step is to request that HEC-RAS compute a flow distribution calculation at the bridge downstream face cross section.
3.10 Calculating Bridge Scour
Autodesk River Analysis can estimate the amount of potential scour at a single opening bridge that can occur during a flood event. bridge upstream face cross section. The software uses the flow distribution feature of HEC-RAS to determine the horizontally distributed flow velocity at the bridge approach cross section and the bridge opening cross section. Leaving this entry blank causes the software to default to an abutment with vertical side slopes. The Broad Crested method is based on work that was done on a trapezoidal shaped broad crested weir (FHWA. and should be selected for situations where roadway overflow will occur due to a spillway flow structure. you must first develop a hydraulic model of the river reach containing the bridge to be analyzed. and should generally be selected since it models typical bridge and culvert crossings. The model should also include several cross sections upstream of the bridge. pier scour. The hydraulic modeling of the bridge should be based upon the procedures discussed in this manual. This model should include several cross sections downstream from the bridge. Once the hydraulic model has been calibrated. 1978).2 percent chance) flood event be used to evaluate the bridge foundation under extreme flooding conditions. In addition to this event.1
Scour Modeling Guidelines
To perform a scour computation at a bridge.
3. Submergence Reduction Method Specifies which method is to be used in reducing the weir flow coefficient due to the submergence effect when weir flow submergence occurs during roadway overflow. thereby determining the total amount of bridge scour. the model should be calibrated to the fullest extent possible. it is recommended that a 500 year (0. From this. This entry is only used for the FHWA WSPRO bridge method for low flow. Flow distributions can be requested at other additional cross sections. This entry represents the number of horizontal units per one vertical unit for the abutment side slope. and the bridge approach cross section. and abutment scour. the modeler can define the flood discharges to be used for the scour analysis. to evaluate the long-term effects of the bridge on the upstream water surface profile.3-46
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Downstream Embankment Slope Specifies the embankment side slope of the bridge abutment (measured in the direction of flow) on the downstream face of the bridge. The scour results can then be drawn onto the bridge opening cross section view. the software can compute the amount of contraction scour. such that any user-defined downstream boundary condition does not affect the hydraulic results inside and just upstream of the bridge.10. The Ogee Method was developed for an ogee spillway shape (COE. the design flood event for a scour analysis is typically the 100 year (1 percent chance) event. showing the effect of the bridge scour.

and therefore should be evaluated prior to performing a bridge scour analysis. Scour Type Specify what type of scour analysis is to be performed.Input Descriptions
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computations. click Define to describe the input data for the scour type. After performing the water surface profile calculations with the flow distributions defined. Flow distributions must be computed in order to get detailed estimates of the depth and velocity at various locations within the cross section. Long-term aggradation and degradation is outside the scope of this software. The software will provide you with a default filename. the Autodesk River Analysis scour computations can then estimate the amount of scour at a bridge opening. as was described in the section titled Scour Modeling Guidelines.
. The Detailed Report option provides complete documentation of the scour analysis. Report Type Specifies the type of scour report to be generated. bridge scour is computed at the bridge downstream cross section. to define the required input data for the scour computations.
3. In the Bridge Scour Calculator dialog box. The input data specifications required to compute scour are defined in the following sections. The total scour at a highway crossing is comprised of four components: • • • • Long-term aggradation and degradation Contraction scour Localized scour at piers Localized scour at abutments
The scour computations allow you to compute contraction scour and localized scour at bridge piers and abutments. Finally. Next. make the bridge downstream face cross section current. on the Scour tab. After selecting the scour type to be computed.2
Defining Scour Data
The first step in computing bridge scour is to perform a successful HEC-RAS analysis. click River tab > Analysis panel > Bridge Scour Calculator. Flow distributions are defined using the Flow Slices data entries in the Section Description dialog box. specify the following parameters: Report Filename Specifies the ASCII text file that the scour report is to be written out to.10. showing every step of the scour computation.

If you ask the software to automatically select the scour equation. To compute contraction scour. the software uses the live-bed contraction scour equation.
. In the Bridge Scour Calculator dialog box. specify the following parameters: All of the data entry variables. that will transport bed material finer than D50. main channel.10. Q2 (optional) Specifies the flow in the left overbank.3-48
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Profile Listing Lists the water surface profiles that are available for computing a scour analysis. and right overbank at the approach cross section. or specify that the software automatically select which equation is appropriate. main channel. are obtained automatically from the HEC-RAS computational results. The approach cross section is the second cross section upstream of the bridge declaration cross section. Scour Equation (optional) Contraction scour can be computed by either the Laursen Live-Bed (Laursen. Otherwise. Y1 (optional) Specifies the average depth (hydraulic depth) in the left overbank. To define data describing the contraction scour modeling parameters. and right overbank at the bridge upstream face cross section. and right overbank at the bridge upstream face cross section. You can change any variable. 1963) contraction scour equations.
3. main channel. main channel.3
Defining Contraction Scour Data
Contraction scour occurs when the flow area of a stream is reduced by a natural contraction or by a bridge opening constriction. and the right overbank at the approach cross section. Vc. Highlight the water surface profile for which you want the scour analysis computed. V1 (optional) Specifies the average flow velocity in the left overbank. the software must compute the critical velocity. 1960) or Laursen Clear-Water (Laursen. the software automatically selects the controlling scour equation. on the Contraction tab. This entry allows you to specify which contraction scour equation is to be used. and a water temperature to compute the K1 factor are required. Y0 (optional) Specifies the average depth in the left overbank. only the D50 grain size (mean size fraction of the bed material). By default. click River tab > Analysis panel > Bridge Scour Calculator. If the average velocity at the approach cross section is greater than Vc. the clearwater scour equation will be used. except K1 and D50.

thereby reducing the rate at which material is removed from the scour hole. and right overbank at the approach cross section for the Laursen Live-Bed equation. then no contraction scour will be computed for the right overbank area. Q1 (optional) Specifies the flow in the left overbank. D50 (required) Specifies the bed material grain size of which 50% are smaller. The software can compute a value for K1. or you can enter a value. K1 (required) Specifies the exponent for the live-bed contraction scour equation that accounts for the mode of bed material transport. main channel. Temp (required) Specifies the water temperature. For example. The Compute K1 for Contraction Scour dialog box is displayed. if there is no right overbank flow inside the bridge. A default water temperature of 60° Fahrenheit is provided.4
Defining Pier Scour Data
Pier scour occurs due to the acceleration of flow around a bridge pier and the formation of flow vortices.10.
. V* (no entry required) Specifies the computed shear velocity at the approach cross section. which remove material from the base of the pier thereby creating a scour hole.
Note
The computation of contraction scour is performed separately for the left overbank. To have the software compute a value. Eventually an equilibrium state is reached between bed material inflow and outflow. These values must be specified by the user. W1 (optional) Specifies the top width of the active flow area (not including the ineffective flow area) at the approach cross section for the Laursen Live-Bed equation. specify the following parameters: S1 (optional) Specifies the computed energy slope at the approach cross section. and right overbank. In the Compute K1 for Contraction Scour dialog box.Input Descriptions
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W2 (optional) Specifies the top width of the active flow area (not including the ineffective flow area) at the bridge upstream face cross section. click Compute. As the depth of scour increases.
3. for the left overbank. main channel. the magnitude of the vortex decreases. W (no entry required) Specifies the fall velocity of the D50 bed material. and the scour hole ceases to grow. and right overbank. This value must be specified by the user. main channel.

click Clear. This entry allows you to specify which pier scour equation is to be used. The software uses the computed flow distribution results to obtain these values. the K1 correction factor for the CSU equation and the Phi correction factor for the Froehlich equation are automatically determined for that pier. You are only required to define the bed condition (K3). The software automatically puts a value in this field based on the bridge input data. You can select a square nose. click Update. you can change any variable to whatever value is appropriate.3-50
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
To define data describing the pier scour modeling parameters. you can change this value. or sharp nose (triangular) pier shape. specify the following parameters: These data entry values are specified on a pier-by-pier basis. To store the user-defined pier data for all piers.
. When you specify a pier nose shape. The local V1 and Y1 is then used to compute the scour for each pier. If Maximum V1 Y1 is selected. et al. click Set All. All other values are obtained automatically from the HEC-RAS computational results or are computed by the software. If necessary. Velocity and Depth Value (optional) Specifies the velocity and depth method to be used in the pier scour calculations. and there is no automatic equation selector since there are application restrictions with the Froehlich equation. However. If Local V1 Y1 is selected. round nose. group of cylinders. To remove user-defined pier data for the currently selected pier. This entry allows you to select either Maximum V1 Y1 or Local V1 Y1. 1990) or the Froehlich (1988) equation (the Froehlich equation is not included in the HEC No. 18 report). The maximum V1 and Y1 is then used for computing scour at all piers. Scour Equation (optional) Pier scour can be computed by either the Colorado State University (CSU) equation (Richardson. In the Bridge Scour Calculator dialog box. the software uses the velocity and depth at the bridge upstream cross section at the centerline stationing for each pier. the software uses the maximum velocity (V1) and depth (Y1) located in the bridge upstream face cross section. on the Pier tab. a (optional) Specifies the pier width. click River tab > Analysis panel > Bridge Scour Data. The CSU equation is the default equation. circular cylinder. To store the user-defined pier data for the currently selected pier. and a D90 size fraction for the bed material. Shape (optional) Specifies the pier nose shape for each pier defined at the bridge opening. The pier selection list is used to select the pier for which to define data.

You can change this value for any individual pier or for all piers. You can change this value for any individual pier or for all piers. If Maximum V1 Y1 is selected for the pier scour calculations. K2 (optional) Specifies the correction factor for angle of attack of the flow on the pier. Also. If Maximum V1 Y1 is selected for the pier scour calculations. when this angle is greater than 5 degrees.Input Descriptions
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D50 (optional) Specifies the bed material grain size of which 50% are smaller. based on what is defined for contraction scour for the left overbank. The software automatically fills in this entry for each pier. and always be entered as positive values.
. and right overbank. then the angle of 90 degrees should be entered. This value is automatically determined by the software from the flow distribution output at the bridge upstream face cross section. This length is used to determine the magnitude of the K2 correction factor. the software sets the K2 correction factor to 1. V1 (optional) Specifies the average velocity of water just upstream of each pier. the pier length (L). L (optional) Specifies the pier length through the bridge. Y1 (optional) Specifies the depth of water just upstream of each pier. Angle (optional) Specifies the angle of attack of the flow approaching the pier. then this field shows for each pier the maximum velocity of water in the cross section. This correction factor is automatically computed by the software once you specify the pier width (a). For example. This value is automatically determined by the software and is set to the defined bridge width. However. then an angle of 0 degrees should be specified. as used in the CSU equation. You can change this value for any individual pier or for all piers. all values should range from 0 to 90. This is the default value for each pier. This value is automatically determined by the software from the flow distribution output at the bridge upstream face cross section. When an angle is entered. This correction factor is automatically determined when you select a pier nose shape. then this field shows for each pier the maximum depth of water in the cross section. main channel. K1 (optional) Specifies the correction factor for pier nose shape. if desired. if the flow direction upstream of the pier is perpendicular to the pier. You can change this value for any individual pier or for all piers. You can change this value for any individual pier or for all piers. if the flow direction upstream of the pier is in-line with the pier. and the angle of attack (Angle).0. Therefore. the software automatically sets a value for the K2 correction factor. as used in the CSU equation.

To define data describing the abutment scour modeling parameters. This correction factor is automatically computed when you select a pier nose shape. a’ (optional) Specifies the projected pier width with respect to the direction of flow.10. and forms a vertical wake vortex at the downstream end of the abutment. as used in the CSU equation. you can override it by specifying a different station value.2 feet (0. This value is automatically computed once the pier width (a). The obstruction of the flow forms a horizontal vortex starting at the upstream end of the abutment and running along the toe of the abutment. on the Abutment tab. K4 (optional) Specifies the factor. This value is used in the Froehlich pier scour equation. small dunes. In the Bridge Scour Calculator dialog box.
3. to decrease scour depths to account for armoring of the scour hole. This factor is only applied when the D50 of the bed material is greater than 0. This value should be defined for each pier in the pier list box. This entry is used to compute the K4 factor. and the depth of water just upstream of the pier. specify the following parameters: Abutment scour is computed separately for the left and right abutment. medium dunes. D90 pier width (a). You can change the value for any variable. if the D90 value has been entered for only the first (leftmost) pier contained in the pier list box. However.3-52
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
K3 (required) Specifies the correction factor for bed condition. If you do not like the stationing that the software picks.5
Defining Abutment Scour Data
Localized scour occurs at bridge abutments when the abutment obstructs the stream flow.06 m). You can select from clear-water scour. plane bed and antidune flow. and pier length (L) values have been entered. and large dunes. BOSS RMS will propagate this same value for all of the other piers when the Bridge Scour Calculator dialog box is closed. This stationing is very important because the hydraulic variables used in the abutment scour computations are obtained from the flow distribution output at this cross section stationing. This factor is automatically calculated by the software. The software automatically selects values for all of the other variables based on the hydraulic output and default settings. click River tab > Analysis panel > Bridge Scour Calculator. vertical. you can change this value. Phi (optional) Specifies the correction factor to be used in the Froehlich equation based upon pier nose shape. and must be specified by the user. and is a function of D50. If necessary. The location of the abutment toe is based on where the roadway embankment intersects the natural ground. vertical with wing walls). flow angle of attack (Angle).
. D90 (required) Specifies the bed material grain size of which 90% are smaller. as used in the CSU equation. You are only required to enter the abutment type (spill-through.

Y1 (optional) Specifies the computed depth of the water at the abutment toe station. The selection is based on computing a factor of the embankment length divided by the approach depth. You can change this value for either the left and/or right abutment. A value of less than 90 degrees should be entered if the abutment is pointing in the downstream direction. or spill-through abutments. You can change this value for either the left and/or right abutment. This value is used in computing the K2 coefficient. the software automatically uses the Froehlich equation. If this factor is equal to or less than 25. The software automatically determines this station value at the point where the roadway embankment and/ or abutment data intersects the natural ground cross section data. if the flow direction upstream of the abutment is perpendicular to the abutment. Length (optional) Specifies the length of the abutment and roadway embankment that is obstructing the flow. For example. A value greater than 90 degrees should be entered if the abutment is pointing in the upstream direction. at the bridge upstream face cross section. The software automatically computes this value for both the left and right embankments. Skew (optional) Specifies the angle of attack of the flow approaching the abutment. then an angle of 90 degrees should be specified. Station at Toe (optional) Specifies the stationing along the upstream face bridge cross section where the toe of the abutment intersects the natural ground. The right embankment length is computed as the stationing of the right extent of the water surface minus the stationing of the right abutment toe at the bridge upstream face cross section (including the ineffective flow area). You can choose between vertical abutments.
. The left embankment length is computed as the stationing of the left abutment toe minus the station of the left extent of the water surface at the bridge upstream face cross section (including the ineffective flow area). By default.Input Descriptions
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Scour Equation (optional) Abutment scour can be computed by either the Froehlich or HIRE equations. or specify that the software automatically select which equation is appropriate. the software automatically uses the HIRE equation. vertical abutments with wing walls. This entry allows you to specify which abutment scour equation is to be used. You can change this value for either the left and/or right abutment. If the factor is greater than 25. the software automatically selects the controlling scour equation. K1 (optional) Specifies the correction factor used to account for the bridge abutment shape. This value is computed by the software as the elevation of the water surface minus the ground elevation at the abutment toe stationing. for use in the HIRE equation.

You can change this value for either the left and/or right abutment. The spillway gate opening height is defined on a profile by profile basis. Ya (optional) Specifies the average depth of flow (hydraulic depth) that is blocked by the embankment at the approach cross section. the software calculates the area left of the left abutment toe and right of the right abutment toe. This value is computed by projecting the abutment toe stationing onto the approach cross section. L’ (optional) Specifies the length of the abutment (embankment) projected normal to the flow. You can change this value for either the left and/or right abutment. this factor increases from a value of one. V1 (optional) Specifies the velocity at the abutment toe. The spillway crest of the gates can
. From the flow distribution output. You can change this value for either the left and/or right abutment. The approach cross section is the second cross section upstream of the bridge declaration cross section. This value is computed by projecting the abutment toe stationing onto the approach cross section. You can change this value for either the left and/or right abutment. You can change this value for either the left and/or right abutment.11 Inline Weirs and Gated Spillways
HEC-RAS can model inline (across the main stream) weirs and controllable gated spillways. From the flow distribution output. This value is automatically computed by the software once an abutment length and a skew angle are entered. the software calculates the area and top width left of the left abutment toe and right of the right abutment toe. This velocity is obtained by finding the velocity in the flow distribution output at the corresponding abutment toe stationing. HEC-RAS can model radial gates (often called tainter gates) and vertical lift gates (sluice gates). determined at the bridge upstream face cross section. This factor is automatically computed by the software. As the skew angle becomes less than 90 degrees. this value becomes less than one. For controllable gated spillways. Ae (optional) Specifies the flow area that is obstructed by the abutment and roadway embankment at the approach cross section. As the skew angle becomes greater than 90 degrees. From the flow distribution output the software calculates the percentage of flow left of the left abutment toe and right of the right abutment toe.3-54
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K2 (optional) Specifies the correction factor to account for the angle of attack of the flow on the abutment. The hydraulic depth is then computed as the area divided by the top width.
3. Qe (optional) Specifies the flow obstructed by the abutment and roadway embankment at the approach cross section. These percentages are multiplied by the total flow to obtain the amount of discharge blocked by each embankment. This value is computed by projecting the abutment toe stationing up to the approach cross section.

An inline weir is required for the inline spillway structure. Use the Inline Spillway dialog box to select what data is to be defined for the inline spillway structure. then the gate control—which defines the gate opening height—must be defined for the gated spillway. Upstream Distance Specifies the distance between the upstream side of the weir structure and the cross section immediately upstream of the structure.1 Example of an inline gated spillway and weir
3. The following sections describe the data used to define an inline spillway structure. but a gated spillway is optional. the spillway structure must be declared at the cross section corresponding to the downstream face of the structure.1
Defining the Spillway Structure
When defining an inline weir and gated spillway structure.2
Defining an Inline Weir Structure
To define an inline spillway structure. click River tab > Input panel > Inline Spillway.11. specify the following parameters: Weir Crest Shape Specifies the type of weir to be analyzed.
3.11.Input Descriptions
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be modeled as either an ogee or broad crested weir shape. The software uses this to determine how much to reduce the weir coefficient due to submergence at the weir. Click Pick to measure the distance from the plan view.11.
. An example of an inline spillway structure is shown in Figure 3.11.1.
Figure 3. In the Inline Spillway dialog box. Select the shape that best matches the weir overflow structure. If a gated spillway is defined. click River tab > Input panel > Inline Spillway. To define an inline spillway structure.

Embankment Slope 1 Specifies the slope of the road embankment on the downstream side of the structure. For an Ogee-shaped spillway. the weir coefficient will fluctuate based upon the actual head going over the weir.
. just upstream of the spillway. then HEC-RAS will use the lowest defined elevation of the weir geometry coordinates for determining when weir flow starts.e. This value should be entered as the horizontal to vertical distance ratio (i. If this parameter is left blank. Click Pick to measure the height from the cross section view. HEC-RAS begins to compute weir flow. Click Pick to define the elevation by selecting it from the cross section view. Design Energy Head This parameter is only required when defining data for an Ogee-shaped weir. The distance between the top of the embankment and the current cross section is equal to the channel reach length of the upstream cross section minus the sum of the weir Width and the Upstream Distance between the embankment and the upstream cross section. minus the mean ground elevation. the weir flow calculations are still based on the actual geometry of the weir and embankment. This value is equal to the energy gradeline elevation (at the specified design discharge) minus the spillway crest elevation.e. Spillway Approach Height This parameter is only required when defining data for an Ogee-shaped weir. This value should be entered as the horizontal to vertical distance ratio (i.. During the weir calculations.3-56
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Width Specifies the width of the embankment top. Embankment Slope 1 Specifies the slope of the weir embankment on the upstream side of the structure. click Compute to compute the weir coefficient at the specified design energy head. Weir Coefficient Specifies the weir coefficient that will be used in the standard weir equation for computing weir flow over the embankment. measured parallel to the stream flow direction. and are not affected by this elevation. However. D. grade) of the embankment slope. U. Click Pick to measure the width from the plan view.S.S. This parameter is equal to the elevation of the spillway crest. grade) of the embankment slope. Min Weir Flow Elevation Specifies the minimum elevation for which weir flow is to begin. The Spillway Approach Height and Design Energy Head parameters must first be specified for the software to compute the weir coefficient. Once the computed upstream energy elevation becomes higher than this elevation..

3. You can also draw the inline weir geometry on the cross section view. Weir Geometry: Horizontal Station and Elevation To add a new weir geometry point. 2. 5. Click River tab > Input panel > Inline Spillway.Input Descriptions
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Click Pick to measure the head from the cross section view. In the Define Gated Spillway dialog box.
3. The new weir geometry point station and elevation values will then be automatically inserted in the data fields. select the point from the list. To draw an inline weir structure: 1. specify the following parameters:
. enter its horizontal station and elevation into the corresponding data fields. see the section titled Drawing the Inline Weir Geometry. To delete a row of data from the list box.11. 4. In the Inline Spillway dialog box. allowing you to quickly alter the elevation for an existing station. select Draw Weir: Enter weir geometry points by clicking anywhere on the section view. right-click the row and click Delete Row(s). To edit an existing weir geometry point.11. 3. For more information. or by typing in station and elevation coordinates (such as 100. select Gated Spillway. Under Define Gated Spillway. 2. with no spaces). To define a gated spillway: 1. 3.3
Drawing the Inline Weir Geometry
Autodesk River Analysis allows you to draw the inline weir geometry on-screen for the currently active cross section view.1320. define the weir geometry. Click River tab > Input panel > Inline Spillway. or click Pick to select it from the current cross section view. an inline weir must first be defined as described in the section titled Defining an Inline Weir Structure on page 3-55. Click Define. Double-clicking on a row of data shown in the list will immediately move the data entry cursor to the weir geometry point data entry.4
Defining a Gated Spillway
In order to define a gated spillway. Click New to draw new weir geometry points from the current cross section view. In the Inline Spillway dialog box.

then this entry is set to 0. A typical value for a radial gate is 0..62.16. The software uses this data entry to determine how much to reduce the weir coefficient due to submergence at the weir. Trunnion Height Specifies the height from the spillway crest to the trunnion pivot point. vertical lift) gates and 0. which is used in the radial gate discharge equation.e.6 to 0. Head Exponent Specifies the upstream energy head exponent. Orifice Coefficient Specifies the submerged orifice coefficient. HEC-RAS uses the free surface flow gate equations.. Discharge Coefficient Specifies the discharge coefficient for the spillway gate opening.e. This coefficient ranges from 0. which is used in the radial gate discharge equation. If the gate opening is between 67 and 80 percent submerged.. All gate opening data within a gate group are identical.72. tainter).e. tainter) gates. vertical lift) and Radial (i. If a sluice gate has been defined. Gate Station Specifies the gate opening centerline stationing. then this entry is set to 1. A different centerline station should be defined for each gate opening within a gate group. except for differing centerline stationing. A typical value is 0. Sluice (i. Gate Group Specifies a set of identical gated spillways. Two gate types are available. Up to 10 different gate groups can be defined at a inline weir structure. which is used for the gate opening when the gate becomes more than 80 percent submerged.3-58
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Gate Type Specifies the type of gated spillway to be analyzed.0 and should not be changed. The total number of identical gates within each gate group is displayed in this list box.e.7 for sluice (i. A typical submerged orifice coefficient value is 0. Select the shape that best matches the weir overflow structure. Trunnion Exponent Specifies the radial gate trunnion height exponent.8 for radial (i.. If a sluice gate has been defined. When the gate opening is less than 67 percent submerged. which is used in the radial gate discharge equation. HEC-RAS uses a transition between the fully submerged orifice equation and the free surface flow gate equations. Opening Exponent Specifies the gate opening exponent.8. A typical value for a radial gate is 0. Click < to define the gate centerline station by picking it from the cross section view.
.5 which is a normal value for a sluice gate. Each gate group can have up to 25 identical gated spillway openings.5 to 0.

5
Defining a Gated Spillway Gate Opening
HEC-RAS allows you to control the spillway gate opening height separately for each gate group on a profile by profile basis. or discharge coefficients. the defined gates are assumed to be completely closed unless a gate opening height has been defined. Select the shape that best matches the weir overflow structure. To do this. the defined spillway gates are assumed to be completely closed unless a gate opening height has been defined. see the section titled Defining a Gated Spillway Gate Opening. elevation. For an Ogee-shaped spillway.11. just upstream of the spillway. size. Broad Crested and Ogee shaped weirs are available. After defining a spillway gate structure using the Define Gated Spillway dialog box. Click Pick to measure the head from the cross section view. then only one gate group needs to be defined.
Defining the Gate Opening Height
After a spillway gate structure is defined. the weir coefficient will fluctuate based upon the actual head going over the weir. This value is equal to the energy gradeline elevation (at the specified design discharge) minus the spillway crest elevation. If the gated spillway openings are different in shape. Click Pick to measure the height from the cross section view. Similarly. This parameter is equal to the elevation of the spillway crest. click Compute to cause BOSS RMS to compute the weir coefficient at the specified design energy head. Weir Coefficient Specifies the weir coefficient that is used in the standard weir equation for computing weir flow over the embankment. then separate gate groups must be defined.
. Design Energy Head This data entry is only required when defining data for an Ogee-shaped weir. minus the mean ground elevation. then additional Gate Groups must be defined. Weir Crest Shape Specifies the type of weir that should be analyzed.
3. The software uses this parameter to determine how much to reduce the weir coefficient due to submergence at the weir. The Spillway Approach Height and Design Energy Head values must first be specified for the software to compute the weir coefficient.Input Descriptions
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If all of the gate openings are exactly the same. if the gates are identical but you want to be able to control the gate openings separately. Note that HEC-RAS allows you to define the spillway gate opening height separately for each gate group on a profile by profile basis. Spillway Approach Height This parameter is only required when defining data for an Ogee-shaped weir. During the weir calculations.

Then. after specifying data for the # Open and Open Height parameters. At the bottom of the Spillway Gate Control dialog box is a list box containing the defined profiles for the HEC-RAS model. click Update to store this data. such as the cross section defining the downstream face of a bridge. The gate group openings are defined separately for each profile. and then select the gate group that the opening height is to be specified for.
3. Therefore. In the Inline Spillway dialog box. it is necessary to first select the profile that the gate opening data is to be defined for. The Floodplain Encroachment dialog box allows you to define the encroachments for the current cross section. that the specified spillway gate opening height is to be applied to. 5. 2. Five different methods are available to define floodplain encroachments. The software’s floodplain encroachment capability should not be confused with the software’s ineffective flow area capability. define the weir geometry.12 Floodplain Encroachments
The software’s floodplain encroachment capability allows the software to analyze encroachments made to the floodplain. Click Control. In the Inline Spillway Gate Openings dialog box. Each method is capable of evaluating the effects of encroachments on bridges and culverts. within the selected gate group.
. 4.
Note
The encroachment analysis can only be performed for profiles 2 through 15 (or whatever number of profiles have been defined by the user). 3. specify the following parameters:
# Opening Specifies the number of openings. Open Height Specifies the spillway gate opening height within the selected gate group. The floodplain encroachment capability is used to analyze changes to the water surface profile due to floodway (or floodplain) encroachments. Encroachments are not performed for the first profile because most of the encroachment methods rely on having a base profile for comparison. such as floodplain fringe development. Click River tab > Input panel > Inline Spillway. This opening height value will be applied to only to the specified number of gate openings. Under Define Gated Spillway. The ineffective flow area capability is used to limit the region of active flow at a specific cross section. select Gated Spillway.3-60
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
To define a gated spillway gate opening: 1.

and 5 feet outside of the right bank station. click River tab > Input panel > Floodplain Encroachments. 4. if you establish a left buffer zone limit of 10 feet and a right buffer zone limit of 5 feet. The default method is to reduce conveyance equally from both overbanks. The default is to have no left or right bank buffer zone. this option has no effect. and will be applied to every cross section and for every profile which has an applicable encroachment method defined. • • If Equal Reduction is selected. if necessary. and Target WS for a range of cross sections in a river reach. All Methods Standard Methods Enables or disables selection of the full range of encroachment methods. For example. 2. Overbank Conveyance Reduction Distribution Specify the conveyance reduction distribution method to use. When the All Methods button is displayed. This specified option is applied globally. Click All Methods.Input Descriptions
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To access the Floodplain Encroachments dialog box. As you switch among different encroachment methods.
Left Bank Offset Right Bank Offset The left and right offsets are used to establish a buffer zone around the main channel for limiting the amount of encroachment. 3. This option is applied globally. the conveyance is eliminated equally from each overbank area. and 5 are available. profile. 4. and Target WS. Select the Reach. This parameter only applies to encroachment methods 3. some of the data entry prompts will change based upon the selected encroachment method. Select Reaches to Display Specify the river reaches in the current model to display in the Encroachment Values table. If Proportional Reduction is selected. and Methods 1. the conveyance is reduced in proportion to the conveyance in each overbank area. The Floodplain Encroachment dialog box allows you to specify any of the five available encroachments methods for any of the profiles listed in the dialog box. Profile. Set Range of Values Specify an encroachment Method.
Encroachment Method
. When you click Set Values. and 5. Downstream XS and Upstream XS. and is applied to every cross section and every profile that has an applicable encroachment method defined. the values are applied to all the cross sections between the specified Downstream XS and Upstream XS. which allows the floodplain encroachments to go right up to the main channel bank stations. only Methods 1 and 4 are available. Method. the software limits all encroachments to up to 10 feet outside of the left bank station. With methods 1 and 2.

Therefore. the HEC-RAS model will correctly mimic the behavior of the original HEC-2 model.
3. The first profile will be the natural (unencroached) profile. 4. Method 4 is first used to compute the approximate floodplain encroachment station locations. the software ignores any encroachment data specified for the current cross section reach. or levees in which flow has been restricted. channel modifications. Method 1 is then used to fine-tune the placement of the floodplain encroachment stations.
Slope Area Profile Computation Method
The slope-area profile computation method of determining the water surface profile cannot be used in conjunction with encroachment methods 3. floodplain encroachments. It knows nothing about ineffective flow areas. or 5 at the furthest downstream cross section (when computing a subcritical flow profile) or for the furthest upstream cross section (when computing a supercritical flow profile). Check to see what encroachment methods have been defined in the model.
Multiple Profiles
HEC-RAS computes the water surface profile for the natural channel (without any encroachments) using the first specified discharge and then computes profiles using the specified encroachments for subsequent discharges. Left Station Specify the left station of the floodplain encroachment
. encroachment analyses require that at least two profiles be specified. Therefore. Therefore. caution should be exercised when applying the Hydraulic Calculator to these situations. if that model is to be analyzed using HEC-RAS.1
Encroachment Method 1
If floodplain encroachment method 1 is selected. then define these encroachments at each cross section. conveyance obstructions. HEC-RAS encroachments must be defined at each cross section where they are to take place. and if the encroachments are meant to be propagated. In that way. Of the five encroachment methods available. and all subsequent profiles will then be encroached. problems can potentially exist if you import a HEC-2 model that has encroachments defined. If None is selected. encroachment methods 1 and 4 are generally the only methods used.
Propagating a Floodplain Encroachment
Note that HEC-RAS does not automatically propagate a defined floodplain encroachment to upstream cross sections. or for a range of cross sections.
Hydraulic Calculator
The Hydraulic Calculator considers the entire cross section geometry as available for flow in its computations.3-62
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
Specify the floodplain encroachment method to be used for each cross section.12. the Left Station and Right Station parameters are available.

Right Station Specify the right station of the floodplain encroachment. Click Pick to graphically measure the encroachment top width to use.
Figure 3.
Figure 3. Click Pick to graphically select the right encroachment station.12. the Fixed top parameter is available.12. These floodplain encroachment bank stations should not be confused with the main channel bank stations.2.12.2
Encroachment Method 2
If floodplain encroachment method 2 is selected.1 Encroachment method 1
3. Fixed Top Specify the top width (or distance) between the two floodplain encroachment bank stations for the current cross section.1.1 Encroachment method 2
.Input Descriptions
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Click Pick to graphically select the left encroachment station.

The specified percentage must be a positive value between 1 and 100.
.2 foot would require an entry of 1.2.12.3.4
Encroachment Method 4
If floodplain encroachment method 4 is selected.12. Target K Specify the percentage of total conveyance to be eliminated from the overbank.12.
Figure 3. a target increase in water surface elevation of 1.1 Encroachment method 3
3.3
Encroachment Method 3
If floodplain encroachment method 3 is selected. the Target WS parameter is available.3-64
Autodesk Project River Analysis 2012 Extension for AutoCAD Civil 3D and Map 3D
3. The specified increase must be positive in value. Target WS The natural cross section will be encroached based on the specified increase in water surface elevation over that computed for natural (un-encroached) conditions. where the total conveyance was computed for natural (un-encroached) conditions. Thus. the Target K parameter is available.

Therefore.Input Descriptions
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Figure 3.2.4 feet is being allowed.5
Encroachment Method 5
If floodplain encroachment method 5 is selected.4.12. as long as the specified maximum change in energy has not been exceeded. if a maximum allowable change of energy of 2. The specified increase must be positive in value. This entry must be positive in value. Target WS The natural cross section will be encroached based on the specified increase in water surface elevation over what was computed for natural (un-encroached) conditions.12.4 should be specified.5. the Target WS and Target EG parameters are available. Thus.2 foot would require an entry of 1.1 Encroachment method 4
3. as described in the previous entry. a target increase in water surface elevation of 1.1 Encroachment Method 5
. Target EG The natural cross section will be encroached based on the specified increase in water surface elevation.12.
Figure 3. then an entry of 2.